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

[Eli Zaretskii <eliz@gnu.org>]

> From: Nicolas Bértolo <nicolasbertolo@gmail.com>
> Date: Sat, 16 May 2020 13:12:20 -0300
> Cc: Andrea Corallo <akrl@sdf.org>, 41242@debbugs.gnu.org
> 
> > I'm not sure I understand why we are talking only about package.el.
> > Wouldn't the same problem happen if the user recompiles a .el file for
> > which a .eln file already exists and is loaded into the session?  
> 
> True, right now the .eln would not be removed. Not even in Posix.

No, on Posix systems we can delete the file, and it will be actually
deleted when its last handle is closed.  I believe this works with
shared libraries as well.

> > And
> > similarly when Emacs is being built and all the *.el files are being
> > compiled or recompiled, sometimes by several Emacs processes running
> > in parallel via "make -jN"
> 
> Help me understand. Are you referring to the case where a developer changes
> an .el file for which an .eln file (now outdated) already exists?

No, I mean building Emacs with "make -j10 bootstrap".

> I think fixing the case above will fix this one.

It's the same problem, yes.  Just a slightly different use case, which
could therefore have different probabilities for some aspects.  For
example, the probability of the same .el file being recompiled from
two separate sessions is relatively small, except when you consider
the "make -jN" use case.