Added a default case to the switch statement in the HEADER FILE to prevent compiler warnings about missing defaults. This change helps avoid compilation breaks when warnings are treated as errors.

(cherry picked from commit 9859c05178)

include/SDL_stdinc.h

@@ -565,6 +565,7 @@ SDL_FORCE_INLINE void SDL_memset4(void *dst, Uint32 val, size_t dwords)
         return;
     }
     switch (dwords % 4) {
+        default:
         case 0: do {    *_p++ = _val;   SDL_FALLTHROUGH;
         case 3:         *_p++ = _val;   SDL_FALLTHROUGH;
         case 2:         *_p++ = _val;   SDL_FALLTHROUGH;