stdinc: On macOS and iOS, use memset_pattern4() for SDL_memset4().

Fixes Bugzilla #4724.

include/SDL_stdinc.h

@@ -420,7 +420,9 @@ extern DECLSPEC void *SDLCALL SDL_memset(SDL_OUT_BYTECAP(len) void *dst, int c,
 /* Note that memset() is a byte assignment and this is a 32-bit assignment, so they're not directly equivalent. */
 SDL_FORCE_INLINE void SDL_memset4(void *dst, Uint32 val, size_t dwords)
 {
-#if defined(__GNUC__) && defined(i386)
+#ifdef __APPLE__
+    memset_pattern4(dst, &val, dwords * 4);
+#elif defined(__GNUC__) && defined(i386)
     int u0, u1, u2;
     __asm__ __volatile__ (
         "cld \n\t"