[tsan] Make tsan_test_util_posix.cc call pthread interceptors on OS X

The tsan_test_util_posix.cc implementation of mutexes call pthread APIs directly, which on OS X don't end up calling the intercepted versions and we miss the synchronization. This patch changes the unit tests to directly call the intercepted versions. This fixes several test failures on OS X.

Differential Revision: http://reviews.llvm.org/D14835

llvm-svn: 253774