SDL_stdinc.h: define _DARWIN_C_SOURCE on macOS for memset_pattern4() hopefully fixes https://bugzilla.libsdl.org/show_bug.cgi?id=5107
diff --git a/include/SDL_stdinc.h b/include/SDL_stdinc.h
index a79354c..97e187f 100644
--- a/include/SDL_stdinc.h
+++ b/include/SDL_stdinc.h
@@ -30,6 +30,10 @@
#include "SDL_config.h"
+#ifdef __APPLE__
+#define _DARWIN_C_SOURCE /* for memset_pattern4() */
+#endif
+
#ifdef HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif