(SSR) Remove compile-time check for _REENTRANT in cxx_thread_policy.h
(SSR) Remove compile-time check for _REENTRANT in cxx_thread_policy.h

This was removed from the rest of the code base in commit
b50218f59ed379ad3645a04bdb37fd72475f5ff4.

Closes #91.

AudioProcessingFramework/apf,AudioProcessingFramework/apf,AudioProcessingFramework/apf