Loading PNG files are part of the core SDL library

Don't disable this functionality when defining SDL_LEAN_AND_MEAN, but if you need to, you can define SDL_DISABLE_STB if you want to compile this out.

Fixes https://github.com/libsdl-org/SDL/issues/15139

src/SDL_internal.h

@@ -191,11 +191,6 @@
 #define SDL_VIDEO_RENDER_SW 1
 #endif
 
-/* STB image conversion */
-#if !defined(SDL_HAVE_STB) && !defined(SDL_LEAN_AND_MEAN)
-#define SDL_HAVE_STB 1
-#endif
-
 /* YUV formats
    - handling of YUV surfaces
    - blitting and conversion functions */

src/video/SDL_stb.c

@@ -23,6 +23,11 @@
 #include "SDL_stb_c.h"
 #include "SDL_surface_c.h"
 
+/* STB image conversion */
+#ifndef SDL_DISABLE_STB
+#define SDL_HAVE_STB
+#endif
+
 #ifdef SDL_HAVE_STB
 ////////////////////////////////////////////////////////////////////////////
 #define malloc SDL_malloc