source: vendor/diffutils/2.8.1/m4/realloc.m4

#serial 5

dnl From Jim Meyering.
dnl Determine whether realloc works when both arguments are 0.
dnl If it doesn't, arrange to use the replacement function.
dnl

AC_DEFUN([jm_FUNC_REALLOC],
[
 dnl xmalloc.c requires that this symbol be defined so it doesn't
 dnl mistakenly use a broken realloc -- as it might if this test were omitted.
 AC_DEFINE(HAVE_DONE_WORKING_REALLOC_CHECK, 1,
           [Define if the realloc check has been performed. ])

 AC_CACHE_CHECK([for working realloc], jm_cv_func_working_realloc,
  [AC_TRY_RUN([
    char *realloc ();
    int
    main ()
    {
      exit (realloc (0, 0) ? 0 : 1);
    }
          ],
         jm_cv_func_working_realloc=yes,
         jm_cv_func_working_realloc=no,
         dnl When crosscompiling, assume realloc is broken.
         jm_cv_func_working_realloc=no)
  ])
  if test $jm_cv_func_working_realloc = no; then
    AC_LIBOBJ(realloc)
    AC_DEFINE(realloc, rpl_realloc,
      [Define to rpl_realloc if the replacement function should be used.])
  fi
])