Cleanup: Split out the WASAPI code into its own file.

Windows/WindowsAudio.cpp

@@ -0,0 +1,19 @@
+#include "Common/OSVersion.h"
+#include "WindowsAudio.h"
+#include "DSoundStream.h"
+#include "WASAPIStream.h"
+
+WindowsAudioBackend *CreateAudioBackend(AudioBackendType type) {
+	if (IsVistaOrHigher()) {
+		switch (type) {
+		case AUDIO_BACKEND_WASAPI:
+		case AUDIO_BACKEND_AUTO:
+			return new WASAPIAudioBackend();
+		case AUDIO_BACKEND_DSOUND:
+		default:
+			return new DSoundAudioBackend();
+		}
+	} else {
+		return new DSoundAudioBackend();
+	}
+}