* lisp/emacs-lisp/cl-macs.el:

* lisp/emacs-lisp/cl-macs.el:
(cl--loop-destr-temps): Remove.
(cl--loop-iterator-function): Rename from cl--loop-map-form and change
its convention.
(cl--loop-set-iterator-function): New function.
(cl-loop): Adjust accordingly, so as not to use cl-subst.
(cl--parse-loop-clause): Adjust all uses of cl--loop-map-form.
Bind `it' with `let' instead of substituting it with `cl-subst'.
(cl--unused-var-p): New function.
(cl--loop-let): Don't use the cl--loop-destr-temps hack any more.
Eliminate some unused variable warnings.