[tsan] Add a DCHECK to verify __tsan_read* and __tsan_write function aren't...

[tsan] Add a DCHECK to verify __tsan_read* and __tsan_write function aren't called from ScopedInterceptor

Interceptors using ScopedInteceptor should never call into user's code before the ScopedInterceptor is out of scope (and its destructor is called). Let's add a DCHECK to enforce that.

Differential Revision: http://reviews.llvm.org/D15381

llvm-svn: 255996