glibc/include/resolv.h

#ifndef _RESOLV_H_

#define RES_SET_H_ERRNO(r,x)			\
  do						\
    {						\
      (r)->res_h_errno = x;			\
      __set_h_errno(x);				\
    }						\
  while (0)

#include <resolv/resolv.h>
#endif