bug#49524: 28.0.50; make-serial-process is not portable

[Eli Zaretskii]

> From: Ken Brown <kbrown@cornell.edu>
> Cc: 49524@debbugs.gnu.org
> Date: Mon, 12 Jul 2021 17:35:40 -0400
> 
> So I should probably remove the reference to non-glibc platforms in my commit 
> message.

Yes, something to the effect of compliance with advertised APIs would
probably be better.

Thanks.