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

[Eli Zaretskii]

> From: Nicolas Bértolo <nicolasbertolo@gmail.com>
> Date: Thu, 14 May 2020 15:00:14 -0300
> Cc: Andrea Corallo <akrl@sdf.org>, 41242@debbugs.gnu.org
> 
> > If you always rename, then you need to always delete, no?
> 
> The Emacs instance that renames the file may not be able to delete the file
> because another Emacs instance may keep an open handle.
> 
> It is this last Emacs instance that should delete the file, not the
> one that renamed it.

Then I guess on Windows we will have to live with the limitation that
a .eln file used by another session cannot be recompiled.

(I must confess that the idea to use libgccjit and shared libraries
for native compilation looks less and less attractive to me due to
these complications.)