bug#41242: Port feature/native-comp to Windows

[Eli Zaretskii]

> From: Andrea Corallo <akrl@sdf.org>
> Cc: Nicolas Bértolo <nicolasbertolo@gmail.com>,
>         41242@debbugs.gnu.org
> Date: Sat, 23 May 2020 08:35:43 +0000
> 
> >> When loading a dump file that contains native compiled elisp we try to 
> >> find the
> >> .eln file. This uses Ffile_exists_p(). This function, in turn, calls
> >> Fexpand_file_name(). This function will use the root directory as
> >> `default_directory' as a fallback.
> >> 
> >> Getting the root directory requires reading the $emacs_dir environment 
> >> variable.
> >> This is setup later in the initialization process. This caused a crash.
> >
> > Can you tell why this doesn't happen when *.elc files are used
> > instead?  Also, what do you mean by "loading a dump file that contains
> > native compiled elisp"? how did native compiled ELisp get into the
> > dump file in the first place?
> 
> Hi Eli,
> 
> you may be interested in this paragraph
> 
> https://akrl.sdf.org/gccemacs.html#orgb063106

Thanks.  I guess this changes a lot in how Emacs starts up?  E.g.,
what happens if the .el file was in the meantime modified and
recompiled into the .eln file? we will load the new versions instead
of the one that was preloaded, right?