bug#59358: 29.0.50; failing to load .eln for init file sets user-init-file to warnings.el

[Eli Zaretskii <eliz@gnu.org>]

> From: Juanma Barranquero <lekktu@gmail.com>
> Date: Fri, 18 Nov 2022 14:17:36 +0100
> 
> If you use ~/.emacs instead of ~.emacs.d/init.el, and happen to compile .emacs, Emacs loads .emacs.elc
> (as it has always done), but the native compiler does *not* know how to compile it (because it does not know
> how to locate its source), so it gives a warning:
> 
> 022-11-18 02:54:01+0100 Warning (comp): Cannot look up eln file as no source file was found for
> d:/Home/.emacs.elc

I think the solution to that is to special-case ".emacs", in
maybe_swap_for_eln, as a file name that doesn't have to have the .el
extension for this purpose.

> and then it assigns the user-init-file to the native-compiled warnings.el,
> 
> "d:/Home/.emacs.d/native/29.0.50-a4a10996/warnings-28e75f4d-02da775e.eln"
> 
> which now, with the fix for bug#59334, ends up pointing to warnings.el:
> 
> ELISP> user-init-file
> "d:/Devel/emacs/repo/trunk/lisp/emacs-lisp/warnings.el"

That is a separate bug, IMO.  Is this because in Fload we set 'found'
to the file name of warnings.el/.eln in this case?  If so, we should
prevent this nonsense.