Make GDK's SDL_main header-only

include/SDL3/SDL_main.h

@@ -54,9 +54,10 @@
 #elif defined(__GDK__)
 /* On GDK, SDL provides a main function that initializes the game runtime.
 
-   Please note that #include'ing SDL_main.h is not enough to get a main()
-   function working. You must either link against SDL3_main or, if not possible,
-   call the SDL_GDKRunApp function from your entry point.
+   If you prefer to write your own WinMain-function instead of having SDL
+   provide one that calls your main() function,
+   #define SDL_MAIN_HANDLED before #include'ing SDL_main.h
+   and call the SDL_GDKRunApp function from your entry point.
 */
 #define SDL_MAIN_NEEDED