AudioCommon: Migrate threadData to OpenALStream and AOSoundStream

This is only ever used in these two sound streams. Seems silly to have it as a class member. Converted it to an atomic as well.

Source/Core/AudioCommon/OpenALStream.h

@@ -4,6 +4,7 @@
 
 #pragma once
 
+#include <atomic>
 #include <thread>
 
 #include "AudioCommon/SoundStream.h"
@@ -72,6 +73,8 @@ public:
 
 private:
 	std::thread thread;
+	std::atomic<bool> m_run_thread;
+
 	Common::Event soundSyncEvent;
 
 	short realtimeBuffer[OAL_MAX_SAMPLES * STEREO_CHANNELS];