sanitizer_common: add thread safety annotations

Enable clang Thread Safety Analysis for sanitizers:
https://clang.llvm.org/docs/ThreadSafetyAnalysis.html

Thread Safety Analysis can detect inconsistent locking,
deadlocks and data races. Without GUARDED_BY annotations
it has limited value. But this does all the heavy lifting
to enable analysis and allows to add GUARDED_BY incrementally.

Reviewed By: melver

Differential Revision: https://reviews.llvm.org/D105716