[TSan] Enable detection of lock-order-inversions for Objective-C @synchronized

Summary:
@synchronized semantics can be synthesized by using existing mutex_[un]lock operations.

```
@synchronized(obj) {
  // ...
}

=> 
{
  mutex_lock(obj);
  // ...
  mutex_unlock(obj);
}
```
Let me know whether you think this a good idea.

Reviewers: dcoughlin, dvyukov, kubamracek, delcypher

Reviewed By: dvyukov

Subscribers: llvm-commits, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D55959

llvm-svn: 350258