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.
- Enables Mac testing on Travis for PR's for project-mac64.
Issue: #1979