Removed memset_pattern4() from SDL headers

This requires including string.h, which isn't always done, so this commit simplifies dependencies on macOS

Fixes https://github.com/libsdl-org/SDL/issues/3657

include/SDL_stdinc.h

@@ -30,12 +30,6 @@
 
 #include "SDL_config.h"
 
-#ifdef __APPLE__
-#ifndef _DARWIN_C_SOURCE
-#define _DARWIN_C_SOURCE 1 /* for memset_pattern4() */
-#endif
-#endif
-
 #ifdef HAVE_SYS_TYPES_H
 #include <sys/types.h>
 #endif
@@ -530,9 +524,7 @@ 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)
 {
-#ifdef __APPLE__
-    memset_pattern4(dst, &val, dwords * 4);
-#elif defined(__GNUC__) && defined(__i386__)
+#if defined(__GNUC__) && defined(__i386__)
     int u0, u1, u2;
     __asm__ __volatile__ (
         "cld \n\t"