Fix -Wundef warnings due to use of unguarded SDL_AUDIO_DRIVER_JACK

src/audio/SDL_audio.c

@@ -82,7 +82,7 @@ static const AudioBootStrap *const bootstrap[] = {
 #ifdef SDL_AUDIO_DRIVER_EMSCRIPTEN
     &EMSCRIPTENAUDIO_bootstrap,
 #endif
-#if SDL_AUDIO_DRIVER_JACK
+#ifdef SDL_AUDIO_DRIVER_JACK
     &JACK_bootstrap,
 #endif
 #if SDL_AUDIO_DRIVER_PIPEWIRE

src/audio/jack/SDL_jackaudio.c

@@ -20,7 +20,7 @@
 */
 #include "SDL_internal.h"
 
-#if SDL_AUDIO_DRIVER_JACK
+#ifdef SDL_AUDIO_DRIVER_JACK
 
 #include "../SDL_audio_c.h"
 #include "SDL_jackaudio.h"