musl/include/stddef.h

#ifndef _STDDEF_H
#define _STDDEF_H

#define NULL 0L

#define __NEED_ptrdiff_t
#define __NEED_size_t
#define __NEED_wchar_t

#include <bits/alltypes.h>

#if __GNUC__ > 3
#define offsetof(type, member) __builtin_offsetof(type, member)
#else
#define offsetof(type, member) ((size_t)( (char *)&(((type *)0)->member) - (char *)0 ))
#endif

#endif