Changelog r12 beta1

Changelog

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Removed all sysroots for pre-GB platform levels. We dropped support for them in r11, but neglected to actually remove them.
Exception handling when using c++_shared on ARM32 now mostly works (see Known Issues). The unwinder will now be linked into each linked object rather than into libc++ itself.
Default compiler flags have been pruned: https://github.com/android-ndk/ndk/issues/27.
- Full changes here: https://android-review.googlesource.com/#/c/207721/5.
-fno-limit-debug-info has been enabled by default for Clang debug builds. This should improve debugability with LLDB.
--build-id is now enabled by default.
- This will be shown in native crash reports so you can easily identify which version of your code was running.
NDK_USE_CYGPATH should no longer cause problems with libgcc: http://b.android.com/195486.
-Wl,--warn-shared-textrel and-Wl,--fatal-warnings are now enabled by default. If you have shared text relocations, your app will not load on Marshmallow or later (and have never been allowed for 64-bit apps).
Precompiled headers should work better: https://github.com/android-ndk/ndk/issues/14 and https://github.com/android-ndk/ndk/issues/16.

Clang has been updated to 3.8svn (r256229, build 2690385).
- Note that Clang packaged in the Windows 64 NDK is actually 32-bit.
__thread should work for real this time.

Synchronized with the ChromeOS GCC @ google/gcc-4_9 r227810.
Backported coverage sanitizer patch from ToT (r231296).
Fixed libatomic to not use ifuncs: https://github.com/android-ndk/ndk/issues/31.

"Erratum 843419 found and fixed" info messages are silenced.
Introduced option '--long-plt' to fix internal linker error when linking huge arm32 binaries.
Fixed wrong run time stubs for AArch64. This was causing jump addresses to be calculated incorrectly for very large DSOs.
Introduced default option '--no-apply-dynamic' to work around a dynamic linker bug for earlier Android releases.
NDK r11 KI for dynamic_cast not working with Clang, x86, stlport_static and optimization has been fixed.

This is not intended to be a comprehensive list of all outstanding bugs.
x86 ASAN still does work. See discussion on https://android-review.googlesource.com/#/c/186276/
Exception unwinding with c++_shared still does not work for ARM on Gingerbread or Ice Cream Sandwich.
Bionic headers and libraries for Marshmallow and N are not yet exposed despite the presence of android-24. Those platforms are still the Lollipop headers and libraries (not a regression from r11).
RenderScript tools are not present (not a regression from r11): https://github.com/android-ndk/ndk/issues/7.
r12 will most likely not work with Android Studio/Gradle right away. The Gradle plugin will need to be updated to match the build changes we made in ndk-build.
We've regressed on http://b.android.com/41770.