bug#29799: 24.5; cl-loop guard clause missing

[Noam Postavsky]

Tino Calancha <tino.calancha@gmail.com> writes:

>     Fix #Bug#29799
>     
>     * lisp/emacs-lisp/cl-macs.el (cl--loop-guard-cond): New variable.
>     (cl--parse-loop-clause): Set it non-nil if the loop contains
>     a for/as clause.
>     (cl-loop): After update the loop variable, update other variables
>     only if cl--loop-guard-cond is non-nil.
>     
>     * test/lisp/emacs-lisp/cl-macs-tests.el (cl-macs-loop-for-as-equals-and):
>     New test.

Looks good, but please add some more info to the summary line.