Swapped out the sound_sync_event.Wait() call by a simple std::sleep_for.

It seems to make no difference besides allowing lower latencies and more
stability on hardware OpenAL cards. Maybe the Wait() call waits for too
long, causing buffers underruns.

Source/Core/AudioCommon/OpenALStream.cpp

@@ -290,7 +290,7 @@ void OpenALStream::SoundLoop()
     palGetSourcei(m_source, AL_BUFFERS_PROCESSED, &num_buffers_processed);
     if (num_buffers_queued == OAL_BUFFERS && !num_buffers_processed)
     {
-      m_sound_sync_event.Wait();
+      std::this_thread::sleep_for(std::chrono::milliseconds(1));
       continue;
     }