i#1979 Mac64: Add 64-bit Mojave + XCode 10.1 build support (#3514)

[derekbruening]

A series of small changes to build with XCode 10.1 64-bit:

• Updates -max_supported_os_version on Mac to 18.
• Updates 64-bit Mac frame field.
• Removes , from runtime options in template defines.
• Removes 32-bit-only tests from the OSX label list for 64-bit.
• Increases the core's preferred base to 0x1'71000000 to stay above
  the default 0x1' _PAGEZERO.
• Adds missing DECL_EXTERNs in mangle_suspend and mangle_asynch tests.
• Adds missing GLOBAL_REFs in common.decode test.
• Re-defines sigcontext_t and uc_mcontext in tools.h to match this toolchain.
• Adds 64-bit libelftc.a and libdwarf.a Mach-O libraries along with
  instructions on how they were built.
• Adds -mmacosx-version-min=10.9 to drcachesim to match core/.
• Fixes a format string warning in drcachesim.

Includes a number of similar small changes from Shawn Denbow's first 2
commits on the project-mac64 branch in PR #2269 and PR #2273, updated for
clang-format:

• Move -vm_base above 4GB since __PAGEZERO takes up first 4GB by default
• Increase MEMQUERY_INTERNAL_DATA_LEN
• Update Mach-O parsing to check for LC_SEGMENT_64
• Change error notifications to warning to allow build to continue
• Define SC_FIELD for 64-bit registers r8-r15 and update references
• Update dynamorio_mach_dep_syscall to use syscall for 64-bit
• Update dynamorio_mach_syscall to use syscall for 64-bit
• Change code referencing eflags to xflags for cross platform compat
• Misc code fix-ups

Issue: #1979