AudioCommon: add Cubeb backend

Source/Core/AudioCommon/CubebStream.h

@@ -0,0 +1,32 @@
+// Copyright 2017 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <cstddef>
+#include <memory>
+
+#include "AudioCommon/SoundStream.h"
+
+#include <cubeb/cubeb.h>
+
+class CubebStream final : public SoundStream
+{
+public:
+  bool Start() override;
+  void Stop() override;
+  void SetVolume(int) override;
+
+private:
+  bool m_stereo = false;
+  cubeb* m_ctx = nullptr;
+  cubeb_stream* m_stream = nullptr;
+
+  std::vector<short> m_short_buffer;
+  std::vector<float> m_floatstereo_buffer;
+
+  static long DataCallback(cubeb_stream* stream, void* user_data, const void* /*input_buffer*/,
+                           void* output_buffer, long num_frames);
+  static void StateCallback(cubeb_stream* stream, void* user_data, cubeb_state state);
+};