tsan: fix deficiency in MutexReadOrWriteUnlock

MutexUnlock uses ReleaseStore on s->clock, which is the right thing to do.
However MutexReadOrWriteUnlock for writers uses Release on s->clock.
Make MutexReadOrWriteUnlock also use ReleaseStore for consistency and performance.
Unfortunately, I don't think any test can detect this as this only potentially
affects performance.

llvm-svn: 335322

compiler-rt/lib/tsan/rtl/tsan_rtl_mutex.cc

@@ -361,7 +361,7 @@ void MutexReadOrWriteUnlock(ThreadState *thr, uptr pc, uptr addr) {
     if (s->recursion == 0) {
       StatInc(thr, StatMutexUnlock);
       s->owner_tid = SyncVar::kInvalidTid;
-      ReleaseImpl(thr, pc, &s->clock);
+      ReleaseStoreImpl(thr, pc, &s->clock);
     } else {
       StatInc(thr, StatMutexRecUnlock);
     }