plug leakage of mutex data. pthread_mutex_destroy() doesnt free our malloc'ed memory.

llvm-svn: 58805

llvm/lib/System/Mutex.cpp

@@ -101,7 +101,7 @@ Mutex::~Mutex()
     pthread_mutex_t* mutex = static_cast<pthread_mutex_t*>(data_);
     assert(mutex != 0);
     pthread_mutex_destroy(mutex);
-    assert(mutex != 0);
+    free(mutex);
   }
 }