bug#28571: 25.3; Compile error on macOS Sierra

[Eli Zaretskii]

> Date: Sun, 24 Sep 2017 12:06:58 +0100
> From: Alan Third <alan@idiocy.org>
> Cc: 28571@debbugs.gnu.org
> 
> diff --git a/src/conf_post.h b/src/conf_post.h
> index febdb8b8bf..dfdb0aa3eb 100644
> --- a/src/conf_post.h
> +++ b/src/conf_post.h
> @@ -397,3 +397,11 @@ extern int emacs_setenv_TZ (char const *);
>  #else
>  # define UNINIT /* empty */
>  #endif
> +
> +/* macOS 10.13 supports futimens and futimesat, older versions don't
> +   but can appear as though they do.  Disable them entirely to avoid
> +   breaking cross-version builds on macOS.  */
> +#ifdef DARWIN_OS
> +# undef HAVE_FUTIMENS
> +# undef HAVE_FUTIMESAT
> +#endif

I think it's preferable to have this stuff localized to the configure
script.  Having the same issue decided in tow different places makes
this harder to maintain.  Can you add an equivalent test to
configure.ac?

Thanks.