bug#52018: 28.0.60; Improve documentation for compilation-finish-functions

[Eli Zaretskii]

> From: Thibault Polge <thibault@thb.lt>
> Cc: 52018@debbugs.gnu.org
> Date: Sun, 21 Nov 2021 21:00:20 +0100
> 
> > I'm asking why do you think they should care.  If they want the
> > process exit status, they can have it, can't they?
> 
> I honestly don't know how to do that, but if they can, I guess all is well.

The function is called with the compilation buffer, right?  And the
compilation process runs in that buffer, right?  So the function can
call get-buffer-process, and then access the exit status via
process-exit-status.