Fix build with older SDL2

source/backend/engine/CarlaEngineSDL.cpp

@@ -27,6 +27,14 @@
 typedef Uint32 SDL_AudioDeviceID;
 #endif
 
+#ifndef SDL_HINT_AUDIO_DEVICE_APP_NAME
+# define SDL_HINT_AUDIO_DEVICE_APP_NAME "SDL_AUDIO_DEVICE_APP_NAME"
+#endif
+
+#ifndef SDL_HINT_AUDIO_DEVICE_STREAM_NAME
+# define SDL_HINT_AUDIO_DEVICE_STREAM_NAME "SDL_AUDIO_DEVICE_STREAM_NAME"
+#endif
+
 CARLA_BACKEND_START_NAMESPACE
 
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