bug#51925: [Trunk][macOS] "vfork" is deprecated

[Eli Zaretskii]

> From: Jacob Faibussowitsch <jacob.fai@gmail.com>
> Date: Wed, 17 Nov 2021 11:50:46 -0600
> 
> This is by no means breaking or disrupting anything on my end (at least that 
> I can tell), but I did notice in
> some commit messages a few weeks that someone was attempting to replace vfork 
> with posix_spawn
> specifically on macOS, so maybe my system is some unhandled corner-case?

That change is already on master.  If your build of a recent master
branch doesn't use the posix_spawn code, the first place to look is in
config.log, where you should try to find the reason(s) why the
configure script decided your system doesn't have posix_spawn.

Thanks.