tsan: add annotations to ignore synchronization operations

The annotations are AnnotateIgnoreSyncBegin/End,
may be useful to ignore some infrastructure synchronization
that introduces lots of false negatives.



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@192355 91177308-0d34-0410-b5e6-96231b3b80d8
tsan: minor refactoring

Replace duplicate code snippet with function.



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@192357 91177308-0d34-0410-b5e6-96231b3b80d8