os0sync.c:

  Backport from 4.0: We had forgotten to call pthread_mutex_destroy when we free an OS mutex in Unix

innobase/os/os0sync.c

@@ -488,7 +488,6 @@ os_fast_mutex_free(
 
 	DeleteCriticalSection((LPCRITICAL_SECTION) fast_mutex);
 #else
-	UT_NOT_USED(fast_mutex);
-
+	pthread_mutex_destroy(fast_mutex);
 #endif
 }