SDL: Add debugging code to output SDL audio driver name being used.

This is to aid with investigation of bug #6510 - "SDL: Audio delay in
daily builds" and similar future issues.

backends/mixer/sdl/sdl-mixer.cpp

@@ -58,6 +58,12 @@ void SdlMixerManager::init() {
 		error("Could not initialize SDL: %s", SDL_GetError());
 	}
 
+	const int maxNameLen = 20;
+	char sdlDriverName[maxNameLen];
+	sdlDriverName[0] = '\0';
+	SDL_AudioDriverName(sdlDriverName, maxNameLen);
+	debug(1, "Using SDL Audio Driver \"%s\"", sdlDriverName);
+
 	// Get the desired audio specs
 	SDL_AudioSpec desired = getAudioSpec(SAMPLES_PER_SEC);