bug#50666: 28.0.50; Fix native compilation on Cygwin

[Eli Zaretskii]

> From: Andrea Corallo <akrl@sdf.org>
> Cc: ASSI <Stromeko@nexgo.de>, 50666@debbugs.gnu.org, kbrown@cornell.edu
> Date: Fri, 24 Sep 2021 07:26:11 +0000
> 
> > Or maybe we should add an automatic fallback on .elc/.el in case
> > loading a .eln fails?  Andrea, WDYT? will that work?
> 
> Yes I think we could have an automatic fallback, we might have
> 'native-elisp-load' (invoked by 'load') re invoke load itself in case of
> failure, not very clean tho.

Is 'native-elisp-load' always called from 'load'?  If so, we could
make it return some special value to signal that fallback is in order,
and then modify 'load' to proceed with loading *.el/*.elc file in that
case.

> But aside the fact that is implementable I think it should be limited to
> just this specific load failure, otherwise it could easily mask other
> issues.

We could log a message in *Messages* about this, so that the fallback
could be discovered.