[PATCH] Add xfchmod to libsupport

[Florian Weimer]

* Alexandra Hájková via Libc-alpha:

> diff --git a/support/Makefile b/support/Makefile
> index f4d157dded..fce5c9cd4a 100644
> --- a/support/Makefile
> +++ b/support/Makefile
> @@ -97,6 +97,7 @@ libsupport-routines = \
>    xdlmopen \
>    xdup2 \
>    xfclose \
> +  xfchmod \
>    xfopen \
>    xfork \
>    xftruncate \

Please keep the list in ASCII order.  Otherwise, this version looks
fine to me, you should push it after sapping xfchmod and xfclose.