Add initial libretro implementation

src/duckstation-libretro/libretro_audio_stream.cpp

@@ -0,0 +1,23 @@
+#include "libretro_audio_stream.h"
+#include "libretro_host_interface.h"
+
+LibretroAudioStream::LibretroAudioStream() = default;
+
+LibretroAudioStream::~LibretroAudioStream() = default;
+
+bool LibretroAudioStream::OpenDevice()
+{
+  m_output_buffer.resize(m_buffer_size * m_channels);
+  return true;
+}
+
+void LibretroAudioStream::PauseDevice(bool paused) {}
+
+void LibretroAudioStream::CloseDevice() {}
+
+void LibretroAudioStream::FramesAvailable()
+{
+  const u32 num_frames = GetSamplesAvailable();
+  ReadFrames(m_output_buffer.data(), num_frames, false);
+  g_retro_audio_sample_batch_callback(m_output_buffer.data(), num_frames);
+}