Sync fc-sdl2.m4 with sdl2.m4 from SDL2-2.24.1
sdl2.m4 has been updated between SDL2-2.24.0 and SDL2-2.24.1. Apply that update to our (modified) copy fc-sdl2.m4
sdl2.m4 has been updated between SDL2-2.24.0 and SDL2-2.24.1. Apply that update to our (modified) copy fc-sdl2.m4