bug#75017: 31.0.50; Untrusted user lisp files

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

> Maybe we should trust the early-init-file as well, but then where does
> this end?  The init files can load gobs of other files.  And there's
> also custom-file (when it isn't nil), desktop-dirname and
> desktop-base-file-name, etc. etc.
> Stefan, WDYT about this?

For Emacs-30, I see no need to make changes to what we have in this
regard for the simple reason that `elisp-flymake-byte-compile` usually
doesn't give great feedback in init files or in most of those other
funny loaded files like desktop's (both false positives and false
negatives).  So there's no hurry in deciding whether to include
`early-init-file`, or `custom-file`, or `desktop-dirname`, or ...

More useful might be to auto-trust the packages's ELisp files
found in `load-path` (because these are files for which that backend
should usually give good quality feedback). But that's a bigger change
and it's not completely clear which files we should trust there, so
I don't think we're ready to add that in `emacs-30`.


        Stefan