bug#65833: 30.0.50; cl-loop on the intervals uses global var

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

Package: Emacs
Version: 30.0.50


    ELISP> (macroexpand '(cl-loop for X being the intervals of B do
                           (FOO)))
    (cl--block-wrapper
     (catch '--cl-block-nil--
       (cl-block --cl-finish--
         (cl--map-intervals
          (lambda (--cl-var1-- --cl-var2--)
            (setq X (cons --cl-var1-- --cl-var2--))
            (FOO))
          B nil nil nil))
       nil))

As you can see, this sets fails to declare `X` as being a local
variable, so it will affect `X` from the surrounding context.

This looping form doesn't exist in Common Lisp, but `for X being` never
behaves like that, so this is clearly a bug.


        Stefan