Use acquire-release semantics for changing deferred updates

alc/alc.cpp

@@ -1621,7 +1621,7 @@ void SetDefaultChannelOrder(ALCdevice *device)
 void ALCcontext::processUpdates()
 {
     std::lock_guard<std::mutex> _{mPropLock};
-    if(mDeferUpdates.exchange(false))
+    if(mDeferUpdates.exchange(false, std::memory_order_acq_rel))
     {
         /* Tell the mixer to stop applying updates, then wait for any active
          * updating to finish, before providing updates.

alc/alcontext.h

@@ -217,7 +217,7 @@ struct ALCcontext : public al::intrusive_ref<ALCcontext> {
      * This does *NOT* stop mixing, but rather prevents certain property
      * changes from taking effect.
      */
-    void deferUpdates() noexcept { mDeferUpdates.store(true); }
+    void deferUpdates() noexcept { mDeferUpdates.exchange(true, std::memory_order_acq_rel); }
 
     /** Resumes update processing after being deferred. */
     void processUpdates();