Remove references to STDC_HEADERS (thanks @sezero!)

include/build_config/SDL_build_config.h.cmake

@@ -52,7 +52,6 @@
 #if HAVE_LIBC
 
 /* Useful headers */
-#cmakedefine STDC_HEADERS 1
 #cmakedefine HAVE_ALLOCA_H 1
 #cmakedefine HAVE_CTYPE_H 1
 #cmakedefine HAVE_FLOAT_H 1

src/SDL_internal.h

@@ -74,7 +74,7 @@
 # include <stdarg.h>
 #endif
 #ifdef HAVE_STRING_H
-# if !defined(STDC_HEADERS) && defined(HAVE_MEMORY_H)
+# ifdef HAVE_MEMORY_H
 #  include <memory.h>
 # endif
 # include <string.h>