Move Cubeb AudioStream to FrontendCommon

This way it doesn't need to be built for libretro.

src/frontend-common/cubeb_audio_stream.h

@@ -0,0 +1,35 @@
+#pragma once
+#include "common/audio_stream.h"
+#include "cubeb/cubeb.h"
+#include <cstdint>
+
+class CubebAudioStream final : public AudioStream
+{
+public:
+  CubebAudioStream();
+  ~CubebAudioStream();
+
+  static std::unique_ptr<AudioStream> Create();
+
+protected:
+  bool IsOpen() const { return m_cubeb_stream != nullptr; }
+
+  bool OpenDevice() override;
+  void PauseDevice(bool paused) override;
+  void CloseDevice() override;
+  void FramesAvailable() override;
+
+  void DestroyContext();
+
+  static long DataCallback(cubeb_stream* stm, void* user_ptr, const void* input_buffer, void* output_buffer,
+                           long nframes);
+  static void StateCallback(cubeb_stream* stream, void* user_ptr, cubeb_state state);
+
+  cubeb* m_cubeb_context = nullptr;
+  cubeb_stream* m_cubeb_stream = nullptr;
+  bool m_paused = true;
+
+#ifdef WIN32
+  bool m_com_initialized_by_us = false;
+#endif
+};