Enable thread safety and libc++ thread safety annotations by default

This sets -Wthread-safety and
-D_LIBCPP_ENABLE_THREAD_SAFETY_ANNOTATIONS by default for all targets
targeting fuchsia. The flags are in the config
//build/config/fuchsia:thread_safety_annotations in the default configuration
set which can be removed by targets that aren't compatible with the
analysis.

Change-Id: I5f3c433f677399c61a7c0fec157ad389440fa10f
1 file changed