Use SDL version of executable icon at runtime on macOS

src/sdl/i_video.c

@@ -42,7 +42,7 @@
 
 #ifdef HAVE_IMAGE
 #include "SDL_image.h"
-#elif defined (__unix__) || defined(__APPLE__) || defined (UNIXCOMMON) // Windows doesn't need this, as SDL will do it for us.
+#elif defined (__unix__) || !defined(__APPLE__) && defined (UNIXCOMMON) // Windows & Mac don't need this, as SDL will do it for us.
 #define LOAD_XPM //I want XPM!
 #include "IMG_xpm.c" //Alam: I don't want to add SDL_Image.dll/so
 #define HAVE_IMAGE //I have SDL_Image, sortof