bug#44743: native-comp: confirm-exit-emacs warns about active processes when compiling

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: Andrea Corallo <akrl@sdf.org>,  stefan@marxist.se,  44743@debbugs.gnu.org
> Date: Tue, 24 Nov 2020 08:52:18 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > FWIW, I think this should be controlled by a user option.  It is not
> > at all obvious that everyone would like compilation processes to be
> > killed automatically, people might want to wait for them to complete.
> 
> Since this is something that Emacs does automatically, in the
> background, I don't think a user option sounds like something somebody
> would want to tweak.

IMO, we should offer an option precisely _because_ this is in
background, thus the user could be unaware of the compilation being
run.  Since compilation takes non-negligible time, I envision users
who'd like to wait for a few moments if that gave them faster Lisp
next time.

This is not unlike background subprocesses about which we do ask on
exit.