LDC 1.25.1

Bug fixes

• druntime: Fix DWARF backtrace segfault regression in case the executable file cannot be opened. (#3677, dlang/druntime#3382)

LDC 1.25.0

(Changes since 1.25.0-beta1 are marked with (new).)

Big news

• Frontend, druntime and Phobos are at version 2.095.1, incl. new command-line option -makedeps. (#3620, #3658, #3668) (new)
• Support for LLVM 12 and LLVM 11.1. (#3663, ldc-developers/druntime#195) (new)
• LLVM for prebuilt packages bumped to v11.0.1. (#3639)
• New prebuilt package for native macOS/arm64 ('Apple silicon'). (#3666) (new)
• LDC invocations can now be nicely profiled via --ftime-trace. (#3624)
• Struct TypeInfos are emitted into referencing object files only, and special TypeInfo member functions into the owning object file only. (#3491)
• Windows:
  • New CI-automated Windows installer corresponding to the multilib package. (#3601)
  • Bundled MinGW-based libs bumped to MinGW-w64 v8.0.0. (#3605)
  • Bundled libcurl upgraded to v7.74.0. (#3638)
  • Breaking ABI changes:
    • extern(D): Pass non-PODs by ref to temporary. (#3612)
    • Win64: Pass/return delegates like slices - in (up to) 2 GP registers. (#3609)
    • Win64 extern(D): Pass/return Homogeneous Vector Aggregates in SIMD registers. (#3610)
• -linkonce-templates comes with a new experimental template emission scheme and is now suited for projects consisting of multiple object files too. It's similar to C++, emitting templated symbols into each referencing compilation unit with optimizer-discardable linkonce_odr linkage. The consequences are manifold - each object file is self-sufficient wrt. templated symbols, naturally working around any template-culling bugs and also meaning increased opportunity for inlining and less need for LTO.
  The probably biggest advantage is that the optimizer can discard unused linkonce_odr symbols early instead of optimizing and forwarding to the assembler. So this is especially useful to decrease compilation times with -O and can at least in some scenarios greatly outweigh the (potentially very much) higher number of symbols defined by the glue layer - on my box, building optimized dub (all-at-once) is 28% faster with -linkonce-templates, and building the optimized Phobos unittests (per module) 56% faster.
  Libraries compiled with -linkonce-templates can generally not be linked against dependent code compiled without -linkonce-templates; the other way around works. (#3600)
• Emit function/delegate literals as linkonce_odr, as they are emitted into each referencing compilation unit too. (#3650) (new)
• Exploit ABI specifics with -preview=in. (#3578)
• Musl: Switch to cherry-picked libunwind-based backtrace alternative. (#3641, ldc-developers/druntime#192) (new)

Platform support

• Supports LLVM 6.0 - 12.0. (new)

Bug fixes

• Fix LTO with -link-internally. The prebuilt Windows packages don't bundle an external lld-link.exe LLD linker anymore. (#2657, #3604)
• Add source location information for TypeInfo diagnostics with -betterC. (#3631, #3632)
• Keep init symbols of built-in TypeInfo classes mutable just like any other TypeInfo, so that e.g. synchronized() can be used on the implicit monitor. (#3599)
• Windows: Fix colliding EH TypeDescriptors for exceptions with the same TypeInfo_Class name. (#3501, #3614)
• Predefine version FreeStanding when targeting bare-metal. (#3607, #3608)
• druntime: Define rt.aaA.AA as naked pointer, no struct wrapper. (#3613)
• Misc. fixes and improvements for the CMake scripts, incl. new defaults for LDC_INSTALL_{LTOPLUGIN,LLVM_RUNTIME_LIBS}. (#3647, #3655, #3654, #3673) (new)
• -cleanup-obj: Put object files into unique temporary directory by default. (#3643, #3660) (new)
• druntime: Add missing core.atomic.atomicFetch{Add,Sub}. (#3646, ldc-developers/druntime#193) (new)
• Fix regression wrt. non-deleted temporary -run executable. (#3636) (new)

Internals

• Ignore -enable-cross-module-inlining if inlining is generally disabled. (#3664) (new)
• Travis CI ported to GitHub Actions (excl. Linux/AArch64). (#3661, #3662) (new)

Known issues

• When building LDC, old LDC 0.17.*/ltsmaster host compilers miscompile LDC ≥ 1.21, leading to potential segfaults of the built LDC. Ltsmaster can still be used to bootstrap a first compiler and then let that compiler compile itself. (#3354)
• Buggy older ld.bfd linker versions may wrongly strip out required symbols, e.g., ModuleInfos (so that e.g. no module ctors/dtors are run). LDC defaults to ld.gold on Linux.
• LDC does not zero the padding area of a real variable. This may lead to wrong results if the padding area is also considered. See #770. Does not apply to real members inside structs etc.

LDC 1.25.0-beta1

Big news

• Frontend, druntime and Phobos are at version 2.095.0+, incl. new command-line option -makedeps. (#3620)
• LLVM for prebuilt packages bumped to v11.0.1. (#3639)
• LDC invocations can now be nicely profiled via --ftime-trace. (#3624)
• Struct TypeInfos are emitted into referencing object files only, and special TypeInfo member functions into the owning object file only. (#3491)
• Windows:
  • New CI-automated Windows installer corresponding to the multilib package. (#3601)
  • Bundled MinGW-based libs bumped to MinGW-w64 v8.0.0. (#3605)
  • Bundled libcurl upgraded to v7.74.0. (#3638)
  • Breaking ABI changes:
    • extern(D): Pass non-PODs by ref to temporary. (#3612)
    • Win64: Pass/return delegates like slices - in (up to) 2 GP registers. (#3609)
    • Win64 extern(D): Pass/return Homogeneous Vector Aggregates in SIMD registers. (#3610)
• -linkonce-templates comes with a new experimental template emission scheme and is now suited for projects consisting of multiple object files too. It's similar to C++, emitting templated symbols into each referencing compilation unit with optimizer-discardable linkonce_odr linkage. The consequences are manifold - each object file is self-sufficient wrt. templated symbols, naturally working around any template-culling bugs and also meaning increased opportunity for inlining and less need for LTO.
  The probably biggest advantage is that the optimizer can discard unused linkonce_odr symbols early instead of optimizing and forwarding to the assembler. So this is especially useful to decrease compilation times with -O and can at least in some scenarios greatly outweigh the (potentially very much) higher number of symbols defined by the glue layer - on my box, building optimized dub (all-at-once) is 28% faster with -linkonce-templates, and building the optimized Phobos unittests (per module) 56% faster.
  Libraries compiled with -linkonce-templates can generally not be linked against dependent code compiled without -linkonce-templates; the other way around works. (#3600)
• Exploit ABI specifics with -preview=in. (#3578)

Platform support

• Supports LLVM 6.0 - 11.0.

Bug fixes

• Fix LTO with -link-internally. The prebuilt Windows packages don't bundle an external lld-link.exe LLD linker anymore. (#2657, #3604)
• Add source location information for TypeInfo diagnostics with -betterC. (#3631, #3632)
• Keep init symbols of built-in TypeInfo classes mutable just like any other TypeInfo, so that e.g. synchronized() can be used on the implicit monitor. (#3599)
• Windows: Fix colliding EH TypeDescriptors for exceptions with the same TypeInfo_Class name. (#3501, #3614)
• Predefine version FreeStanding when targeting bare-metal. (#3607, #3608)
• druntime: Define rt.aaA.AA as naked pointer, no struct wrapper. (#3613)

Known issues

• When building LDC, old LDC 0.17.*/ltsmaster host compilers miscompile LDC ≥ 1.21, leading to potential segfaults of the built LDC. Ltsmaster can still be used to bootstrap a first compiler and then let that compiler compile itself. (#3354)
• Buggy older ld.bfd linker versions may wrongly strip out required symbols, e.g., ModuleInfos (so that e.g. no module ctors/dtors are run). LDC defaults to ld.gold on Linux.
• LDC does not zero the padding area of a real variable. This may lead to wrong results if the padding area is also considered. See #770. Does not apply to real members inside structs etc.

LDC 1.24.0

(Changes since 1.24.0-beta1 are marked with (new).)

Big news

• Frontend, druntime and Phobos are at version 2.094.1+, incl. new command-line options -cov=ctfe, -vtemplates=list-instances and -HC=<silent|verbose> . (#3560, #3582, #3588, #3593) (new)
• Support for LLVM 11. The prebuilt packages use v11.0.0; x86 packages newly include the LLVM backend for AMD GPUs. (#3546, #3586) (new)
• Experimental support for macOS on 64-bit ARM, thanks Guillaume! All druntime/Phobos unit tests pass. The macOS package includes prebuilt druntime/Phobos; adapt the SDK path in etc/ldc2.conf and then use -mtriple=arm64-apple-macos to cross-compile. If you know how to work around the countless linker warnings, please let us know. (dlang/druntime#3226, #3583) (new)

Platform support

• Supports LLVM 6.0 - 11.0.

Bug fixes

• Fix potentially wrong context pointers when calling delegate literals. (#3553, #3554)
• Fix alignment issue when casting vector rvalue to static array. (c8889a9)
• Make sure lambdas in pragma(inline, true) functions are emitted into each referencing compilation unit. (#3570)
• Fix -Xcc=-Wl,... by dropping support for comma-separated list of cc options. (c61b135) (new)
• Fix ThreadSanitizer support by not detaching main thread upon program termination. (#3572) (new)
• Traverse full chain of nested aggregates when resolving a nested variable. (#3556, #3558) (new)

Internals

• CI: Linux AArch64 is now also tested by a Travis job, because Shippable has sadly become unreliable. (#3469)
• Building LDC with an LDC host compiler might be somewhat faster now (requires -DLDC_LINK_MANUALLY=OFF in the CMake command-line on non-Windows hosts). (#3575) (new)

Known issues

• When building LDC, old LDC 0.17.*/ltsmaster host compilers miscompile LDC ≥ 1.21, leading to potential segfaults of the built LDC. Ltsmaster can still be used to bootstrap a first compiler and then let that compiler compile itself. (#3354)
• Buggy older ld.bfd linker versions may wrongly strip out required symbols, e.g., ModuleInfos (so that e.g. no module ctors/dtors are run). LDC defaults to ld.gold on Linux.
• LDC does not zero the padding area of a real variable. This may lead to wrong results if the padding area is also considered. See #770. Does not apply to real members inside structs etc.

LDC 1.24.0-beta1

Big news

• Frontend, druntime and Phobos are at version 2.094.0+, incl. new command-line options -cov=ctfe, -vtemplates=list-instances and -HC=<silent|verbose> . (#3560)
• Support for LLVM 11; the prebuilt packages use a very recent build (v11.0.0-rc4+) as LLVM 11 hasn't been finalized yet. The prebuilt x86 packages newly include the LLVM backend for AMD GPUs. (#3546)

Platform support

• Supports LLVM 6.0 - 11.0.

Bug fixes

• Fix potentially wrong context pointers when calling delegate literals. (#3553, #3554)
• Fix alignment issue when casting vector rvalue to static array. (c8889a9)
• Make sure lambdas in pragma(inline, true) functions are emitted into each referencing compilation unit. (#3570)

Internals

• CI: Linux AArch64 is now also tested by a Travis job, because Shippable has sadly become unreliable. (#3469)

Known issues

• When building LDC, old LDC 0.17.*/ltsmaster host compilers miscompile LDC ≥ 1.21, leading to potential segfaults of the built LDC. Ltsmaster can still be used to bootstrap a first compiler and then let that compiler compile itself. (#3354)
• Buggy older ld.bfd linker versions may wrongly strip out required symbols, e.g., ModuleInfos (so that e.g. no module ctors/dtors are run). LDC defaults to ld.gold on Linux.
• LDC does not zero the padding area of a real variable. This may lead to wrong results if the padding area is also considered. See #770. Does not apply to real members inside structs etc.

LDC 1.23.0

(Changes since 1.23.0-beta1 are marked with (new).)

Big news

• Frontend, druntime and Phobos are at version 2.093.1+, incl. new command-line option -vtemplates. (#3476, #3538, #3541) (new)
• Min required LLVM version raised to v6.0, dropping support for v3.9-5.0. (#3493)
• LLVM for prebuilt packages bumped to v10.0.1. (#3513) (new)
• The prebuilt Mac package now also includes prebuilt druntime/Phobos for the iOS/x86_64 simulator, making cross-compilation work out of the box with -mtriple=x86_64-apple-ios12.0. (#3478)
• Windows: New -gdwarf CLI option to emit DWARF debuginfos for MSVC targets, e.g., for debugging with gdb/lldb. (#3533) (new)
• New -platformlib CLI option to override the default linked-with platform libraries, e.g., when targeting bare-metal. (#3374, #3475) (new)

Platform support

• Supports LLVM 6.0 - 10.0.

Bug fixes

• Fix regression since v1.22: shared druntime potentially overriding libstdc++ symbols and breaking exceptions in C++ libraries. (#3530, #3537) (new)
• Fix naked DMD-style asm emission for non-Mac x86 Darwin targets (e.g., iOS simulators). (#3478)
• -betterC: Don't use unsupported EH for handling clean-ups. (#3479, #3482)
• dcompute: Fix wrong address space loads and stores. Thx Rob! (#3428)
• Fix ICE wrt. missing IR declarations for some forward-declared functions. (#3496, #3503)
• Fix ICE wrt. inline IR and empty parameter types tuple. (#3509) (new)
• Fix PGO issues. (#3375, #3511, #3512, #3524) (new)
• Improve support for LLVM's ThreadSanitizer. (#3522) (new)
• Fix linker cmdline length limitation via response files. (#3535, #3536) (new)

Internals

• Compiler performance wrt. string literals emission has been improved. Thx @looked-at-me! (#3490, #3492)
• Link libstdc++ statically for libldc-jit.so of prebuilt Linux packages, to increase portability. (#3473, #3474)
• Set up Visual D when using the Visual Studio CMake generator, making LDC compiler development on Windows a smooth out-of-the-box experience. (#3494)

Known issues

• When building LDC, old LDC 0.17.*/ltsmaster host compilers miscompile LDC ≥ 1.21, leading to potential segfaults of the built LDC. Ltsmaster can still be used to bootstrap a first compiler and then let that compiler compile itself. (#3354)
• Buggy older ld.bfd linker versions may wrongly strip out required symbols, e.g., ModuleInfos (so that e.g. no module ctors/dtors are run). LDC defaults to ld.gold on Linux.
• LDC does not zero the padding area of a real variable. This may lead to wrong results if the padding area is also considered. See #770. Does not apply to real members inside structs etc.

LDC 1.23.0-beta1

Big news

• Frontend, druntime and Phobos are at version 2.093.0+, incl. new command-line option -vtemplates. (#3476)
• Min required LLVM version raised to v6.0, dropping support for v3.9-5.0. (#3493)
• The prebuilt Mac package now also includes prebuilt druntime/Phobos for the iOS/x86_64 simulator, making cross-compilation work out of the box with -mtriple=x86_64-apple-ios12.0. (#3478)

Platform support

• Supports LLVM 6.0 - 10.0.

Bug fixes

• Fix naked DMD-style asm emission for non-Mac x86 Darwin targets (e.g., iOS simulators). (#3478)
• -betterC: Don't use unsupported EH for handling clean-ups. (#3479, #3482)
• dcompute: Fix wrong address space loads and stores. Thx Rob! (#3428)
• Fix ICE wrt. missing IR declarations for some forward-declared functions. (#3496, #3503)

Internals

• Compiler performance wrt. string literals emission has been improved. Thx @looked-at-me! (#3490, #3492)
• Link libstdc++ statically for libldc-jit.so of prebuilt Linux packages, to increase portability. (#3473, #3474)
• Set up Visual D when using the Visual Studio CMake generator, making LDC compiler development on Windows a smooth out-of-the-box experience. (#3494)

Known issues

• When building LDC, old LDC 0.17.*/ltsmaster host compilers miscompile LDC ≥ 1.21, leading to potential segfaults of the built LDC. Ltsmaster can still be used to bootstrap a first compiler and then let that compiler compile itself. (#3354)
• Buggy older ld.bfd linker versions may wrongly strip out required symbols, e.g., ModuleInfos (so that e.g. no module ctors/dtors are run). LDC defaults to ld.gold on Linux.
• LDC does not zero the padding area of a real variable. This may lead to wrong results if the padding area is also considered. See #770. Does not apply to real members inside structs etc.

LDC 1.22.0

(Changes since 1.22.0-beta2 are marked with (new).)

Big news

• Frontend, druntime and Phobos are at version 2.092.1+. (#3413, #3416, #3429, #3434, #3452, #3467) (new)
• AArch64: All known ABI issues have been fixed. C(++) interop should now be on par with x86_64, and variadics usable with core.{vararg,stdc.stdarg}. (#3421)
• Windows hosts: DMD's Visual C++ toolchain detection has been adopted. As that's orders of magnitude faster than the previous method involving the MS batch file, auto-detection has been enabled by default, so if you have a non-ancient Visual C++ installation, it will now be used automatically for linking. The environment setup has been reduced to the bare minimum (LIB and PATH). (#3415)
• FreeBSD x64: CI with CirrusCI is now fully green and includes automated prebuilt package generation. The package depends on the llvm ports package and should currently work on FreeBSD 11-13. (#3453, #3464) (new)
• Link-time overridable @weak functions are now emulated for Windows targets and work properly for ELF platforms. For ELF, LDC doesn't emit any COMDATs anymore. (#3424)
• New ldc.gccbuiltins_{amdgcn,nvvm} for AMD GCN and NVIDIA PTX targets. (#3411)
• druntime: Significant speed-up for core.math.ldexp. (#3440, #3446)

Platform support

• Supports LLVM 3.9 - 10.0.

Bug fixes

• Cross-module inlining (incl. pragma(inline, true)): Enable emission into multiple object files. This may have a significant impact on performance (incl. druntime/Phobos) when not using LTO. (#3126, #3442)
• Android: Fix TLS initialization regression (introduced in v1.21) and potential alignment issues. Unfortunately, the ld.bfd linker is required for our custom TLS emulation scheme, unless you're willing to use a custom linker script. So -linker=bfd is the new default for Android targets. (#3462) (new)
• Casting (static and dynamic) arrays to vectors now loads the data instead of splatting the first element. (#3418, #3419)
• Fix return statements potentially accessing memory from destructed temporaries. (#3426)
• Add proper support for -checkaction=halt. (#3430, #3431)
• druntime: Include core.stdcpp.* modules. (#3103, #3158)
• GCC-style asm: Add support for indirect input operands ("m"). (#3438)
• FreeBSD: Fix backtraces for optimized code by switching to external libexecinfo. (#3108, #3453)
• FreeBSD: Fix C math related issues (incl. CTFE math issues) by bringing core.stdc.{math,tgmath} up to speed. (dlang/druntime#3119)
• Fix ICE for captured parameters not passed on the LLVM level. (#3441)
• Convenience fixes for RISC-V and other exotic targets. (#3457, #3460) (new)

Internals

• When printing compile-time reals to hex strings (mangling, .di headers), LDC now uses LLVM instead of the host C runtime, for proper and consistent results. (#3410)
• One limitation for exotic hosts wrt. C long double precision has been lifted. (#3414)
• For AVR targets, the compiler now predefines AVR and emits all TLS globals as regular __gshared ones. (#3420)
• WebAssembly: New memory grow/size intrinsics. (ldc-developers/druntime#187) (new)
• New -fno-plt option to avoid PLT external calls. (#3443)
• iOS/arm64 CI, running the debug druntime & Phobos unittests on an iPhone 6S. Thx Jacob for this tedious work! (#3379, #3450)

Known issues

• When building LDC, old LDC 0.17.*/ltsmaster host compilers miscompile LDC ≥ 1.21, leading to potential segfaults of the built LDC. Ltsmaster can still be used to bootstrap a first compiler and then let that compiler compile itself. (#3354)
• Buggy older ld.bfd linker versions may wrongly strip out required symbols, e.g., ModuleInfos (so that e.g. no module ctors/dtors are run). LDC defaults to ld.gold on Linux.
• LDC does not zero the padding area of a real variable. This may lead to wrong results if the padding area is also considered. See #770. Does not apply to real members inside structs etc.

LDC 1.22.0-beta2

(Changes since 1.22.0-beta1 are marked with (new).)

Big news

• Frontend, druntime and Phobos are at version 2.092.0+. (#3413, #3416, #3429, #3434, #3452) (new)
• AArch64: All known ABI issues have been fixed. C(++) interop should now be on par with x86_64, and variadics usable with core.{vararg,stdc.stdarg}. (#3421)
• Windows hosts: DMD's Visual C++ toolchain detection has been adopted. As that's orders of magnitude faster than the previous method involving the MS batch file, auto-detection has been enabled by default, so if you have a non-ancient Visual C++ installation, it will now be used automatically for linking. The environment setup has been reduced to the bare minimum (LIB and PATH). (#3415)
• Link-time overridable @weak functions are now emulated for Windows targets and work properly for ELF platforms. For ELF, LDC doesn't emit any COMDATs anymore. (#3424)
• New ldc.gccbuiltins_{amdgcn,nvvm} for AMD GCN and NVIDIA PTX targets. (#3411)
• druntime: Significant speed-up for core.math.ldexp. (#3440, #3446) (new)

Platform support

• Supports LLVM 3.9 - 10.0.

Bug fixes

• Cross-module inlining (incl. pragma(inline, true)): Enable emission into multiple object files. (#3126, #3442) (new)
• Casting (static and dynamic) arrays to vectors now loads the data instead of splatting the first element. (#3418, #3419)
• Fix return statements potentially accessing memory from destructed temporaries. (#3426)
• Add proper support for -checkaction=halt. (#3430, #3431)
• druntime: Include core.stdcpp.* modules. (#3103, #3158) (new)
• GCC-style asm: Add support for indirect input operands ("m"). (#3438) (new)
• FreeBSD: Fix backtraces for optimized code by switching to external libexecinfo. (#3108, #3453) (new)
• FreeBSD: Fix C math related issues (incl. CTFE math issues) by bringing core.stdc.{math,tgmath} up to speed. (dlang/druntime#3119) (new)
• Fix ICE for captured parameters not passed on the LLVM level. (#3441) (new)

Internals

• When printing compile-time reals to hex strings (mangling, .di headers), LDC now uses LLVM instead of the host C runtime, for proper and consistent results. (#3410)
• One limitation for exotic hosts wrt. C long double precision has been lifted. (#3414)
• For AVR targets, the compiler now predefines AVR and emits all TLS globals as regular __gshared ones. (#3420)
• New -fno-plt option to avoid PLT external calls. (#3443) (new)
• iOS/arm64 CI, running the debug druntime & Phobos unittests on an iPhone 6S. Thx Jacob for this tedious work! (#3379, #3450) (new)
• FreeBSD CI with CirrusCI is now fully green and non-optional. (#3453) (new)

Known issues

• When building LDC, old LDC 0.17.*/ltsmaster host compilers miscompile LDC ≥ 1.21, leading to potential segfaults of the built LDC. Ltsmaster can still be used to bootstrap a first compiler and then let that compiler compile itself. (#3354)
• Buggy older ld.bfd linker versions may wrongly strip out required symbols, e.g., ModuleInfos (so that e.g. no module ctors/dtors are run). LDC defaults to ld.gold on Linux.
• LDC does not zero the padding area of a real variable. This may lead to wrong results if the padding area is also considered. See #770. Does not apply to real members inside structs etc.

LDC 1.22.0-beta1

Big news

• Frontend, druntime and Phobos are at version 2.092.0+. (#3413, #3416, #3429, #3434)
• AArch64: All known ABI issues have been fixed. C(++) interop should now be on par with x86_64, and variadics usable with core.{vararg,stdc.stdarg}. (#3421)
• Windows hosts: DMD's Visual C++ toolchain detection has been adopted. As that's orders of magnitude faster than the previous method involving the MS batch file, auto-detection has been enabled by default, so if you have a non-ancient Visual C++ installation, it will now be used automatically for linking. The environment setup has been reduced to the bare minimum (LIB and PATH). (#3415)
• Link-time overridable @weak functions are now emulated for Windows targets and work properly for ELF platforms. For ELF, LDC doesn't emit any COMDATs anymore. (#3424)
• New ldc.gccbuiltins_{amdgcn,nvvm} for AMD GCN and NVIDIA PTX targets. (#3411)

Platform support

• Supports LLVM 3.9 - 10.0.

Bug fixes

• Casting (static and dynamic) arrays to vectors now loads the data instead of splatting the first element. (#3418, #3419)
• Fix return statements potentially accessing memory from destructed temporaries. (#3426)
• Add proper support for -checkaction=halt. (#3430, #3431)

Internals

• When printing compile-time reals to hex strings (mangling, .di headers), LDC now uses LLVM instead of the host C runtime, for proper and consistent results. (#3410)
• One limitation for exotic hosts wrt. C long double precision has been lifted. (#3414)
• For AVR targets, the compiler now predefines AVR and emits all TLS globals as regular __gshared ones. (#3420)

Known issues

• When building LDC, old LDC 0.17.*/ltsmaster host compilers miscompile LDC ≥ 1.21, leading to potential segfaults of the built LDC. Ltsmaster can still be used to bootstrap a first compiler and then let that compiler compile itself. (#3354)
• Buggy older ld.bfd linker versions may wrongly strip out required symbols, e.g., ModuleInfos (so that e.g. no module ctors/dtors are run). LDC defaults to ld.gold on Linux.
• LDC does not zero the padding area of a real variable. This may lead to wrong results if the padding area is also considered. See #770. Does not apply to real members inside structs etc.