remove '#include <stddef.h>'

Author: ziqingluo-90

clang/test/Sema/attr-nonstring_safe.c

@@ -21,9 +21,9 @@ char32_t c32foo[3] = U"fo\0"; // cxx-error {{initializer-string for char array i
 #else
 
 // In C, the following examples are fine:
-#include <stddef.h>
 typedef unsigned short char16_t;
 typedef unsigned int char32_t;
+typedef int wchar_t;
 
 char foo3[3] = "fo\0";
 char foo1[1] = "\0";