[tsan] Modify the tls_race.cc and tls_race2.cc tests to pass on OS X

On OS X, __thread variables are lazily heap-allocated (with malloc). Therefore, they're recognized as heap blocks (which is what they are) and not as TLS variables in TSan reports. Figuring out if a heap block is a TLS or not is difficult (in malloc interceptor we could analyze the caller and then mark the object), so let's instead modify the tests so that we expect the report to say "Location is heap block" instead of "Location is TLS".

Differential Revision: http://reviews.llvm.org/D14873

llvm-svn: 253858