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/AOSoundStream.h

@@ -4,6 +4,7 @@
 
 #pragma once
 
+#include <atomic>
 #include <mutex>
 #include <thread>
 
@@ -19,6 +20,7 @@ class AOSound final : public SoundStream
 {
 #if defined(HAVE_AO) && HAVE_AO
 	std::thread thread;
+	std::atomic<bool> m_run_thread;
 	std::mutex soundCriticalSection;
 	Common::Event soundSyncEvent;