bug#67523: check-declare doesn't account for shorthands

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

On Emacs 29.1, when running `check-declare-file' on a file with
`declare-function' forms, I get

Warning (check-declare): said ‘some-nice-string-utils-foobar’ was defined in
some-nice-string-utils.el: function not found

The problem is that `check-declare-verify' attempts to search for the
full symbol name using this regular expression:

(setq re (format (if cflag
                     "^[ \t]*\\(DEFUN\\)[ \t]*([ \t]*\"%s\""
                   "^[ \t]*(\\(fset[ \t]+'\\|\
cl-def\\(?:generic\\|method\\|un\\)\\|\
def\\(?:un\\|subst\\|foo\\|method\\|class\\|\
ine-\\(?:derived\\|generic\\|\\(?:global\\(?:ized\\)?-\\)?minor\\)-mode\\|\
\\(?:ine-obsolete-function-\\)?alias[ \t]+'\\|\
ine-overloadable-function\\)\\)\
[ \t]*%s\\([ \t;]+\\|$\\)")
                 (regexp-opt (mapcar 'cadr fnlist) t)))
(while (re-search-forward re nil t)
  ...
  )

where (mapcar 'cadr fnlist) is the full symbol name.

Since the full symbol name never appears in the file in which it was
defined, re-search-forward never finds it, and so "function not found".

A potential solution could be to convert the longhand symbol into its
shorthand form and pass that into re-search-forward.  This is tricky
since there may be multiple different shorthands which could yield the
same longhand form.  It might be more feasible to run re-search-forward
on a known common suffix portion of the symbol name, then with point on
the suspected definition, run `intern-soft' to get the full symbol name.

A workaround is to not use shorthands in function definitions.

Thoughts?

Joseph