Fix CMake build

src/duckstation/CMakeLists.txt

@@ -2,6 +2,8 @@ set(SRCS
   main.cpp
   sdl_audio_mixer.cpp
   sdl_audio_mixer.h
+  sdl_audio_stream.cpp
+  sdl_audio_stream.h
   sdl_interface.cpp
   sdl_interface.h
 )