Fix -Wundef warnings due to use of unguarded SDL_AUDIO_DRIVER_COREAUDIO

src/audio/SDL_audio.c

@@ -55,7 +55,7 @@ static const AudioBootStrap *const bootstrap[] = {
 #ifdef SDL_AUDIO_DRIVER_HAIKU
     &HAIKUAUDIO_bootstrap,
 #endif
-#if SDL_AUDIO_DRIVER_COREAUDIO
+#ifdef SDL_AUDIO_DRIVER_COREAUDIO
     &COREAUDIO_bootstrap,
 #endif
 #if SDL_AUDIO_DRIVER_AAUDIO

src/audio/coreaudio/SDL_coreaudio.m

@@ -20,7 +20,7 @@
 */
 #include "SDL_internal.h"
 
-#if SDL_AUDIO_DRIVER_COREAUDIO
+#ifdef SDL_AUDIO_DRIVER_COREAUDIO
 
 /* !!! FIXME: clean out some of the macro salsa in here. */