bug#46256: [feature/native-comp] AOT eln files ignored if run from build tree

[Eli Zaretskii]

> From: Andrea Corallo <akrl@sdf.org>
> Cc: Eli Zaretskii <eliz@gnu.org>, 46256@debbugs.gnu.org,
>         andrewjmoreton@gmail.com
> Date: Tue, 09 Mar 2021 08:32:46 +0000
> 
> The original code was written in the assumption that dlclose (as
> FreeLibrary) can't fail unloading a shared when the internal refcount
> goes to zero.  As this is not the case

I think it _is_ the case, but the problem might be that the refcount
is not zero, and therefore the shared library is not actually unloaded
and unmapped.  (I say "might be" because I still don't see the
scenario where this could happen, and I'm not sure if it does happen
the solution should be as suggested -- it could be that it's better to
not load the .eln the second time, i.e. make 'load' behave like
'require').