[tsan] Add interceptors for objc_sync_enter and objc_sync_exit

Objective-C's @synchronize synchronization primitive uses calls to objc_sync_enter and objc_sync_exit runtime functions. In most cases, they end up just calling pthread_mutex_lock/pthread_mutex_unlock, but there are some cases where the synchronization from pthread_mutex_lock/pthread_mutex_unlock interceptors isn't enough. Let's add explicit interceptors for objc_sync_enter and objc_sync_exit to handle all cases.

Differential Revision: https://reviews.llvm.org/D45487

llvm-svn: 329982