tsan: be silent if verbosity=0

Currently tests fail with:
Check failed: 'AAA' == 'AAA ==26017==Could not detach from thread 361395 (errno 3).'



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@192711 91177308-0d34-0410-b5e6-96231b3b80d8