Provide generalized variables in core Elisp.

Provide generalized variables in core Elisp.
* lisp/emacs-lisp/gv.el: New file.
* lisp/subr.el (push, pop): Extend to generalized variables.
* lisp/loadup.el (macroexp): Unload if preloaded and uncompiled.
* lisp/emacs-lisp/cl-lib.el (cl-pop, cl-push, cl--set-nthcdr): Remove.
* lisp/emacs-lisp/cl-macs.el: Require gv.  Use gv-define-setter,
gv-define-simple-setter, and gv-define-expander.
Remove setf-methods defined in gv.  Rename cl-setf -> setf.
(cl-setf, cl-do-pop, cl-get-setf-method): Remove.
(cl-letf, cl-letf*, cl-define-modify-macro, cl-defsetf)
(cl-define-setf-expander, cl-struct-setf-expander): Move to cl.el.
(cl-remf, cl-shiftf, cl-rotatef, cl-callf, cl-callf2): Rewrite with
gv-letplace.
(cl-defstruct): Don't define setf-method any more.
* lisp/emacs-lisp/cl.el (flet): Don't autoload.
(cl--letf, letf, cl--letf*, letf*, cl--gv-adapt)
(define-setf-expander, defsetf, define-modify-macro)
(cl-struct-setf-expander): Move from cl-lib.el.
* lisp/emacs-lisp/syntax.el:
* lisp/emacs-lisp/ewoc.el:
* lisp/emacs-lisp/smie.el:
* lisp/emacs-lisp/cconv.el:
* lisp/emacs-lisp/timer.el: Rename cl-setf -> setf, cl-push -> push.
(timer--time): Use gv-define-simple-setter.
* lisp/emacs-lisp/macroexp.el (macroexp-let2): Rename from macroexp-let²
to avoid coding-system problems in subr.el.  Adjust all users.
(macroexp--maxsize, macroexp-small-p): New functions.
* lisp/emacs-lisp/bytecomp.el (byte-compile-file): Don't use cl-letf.
* lisp/scroll-bar.el (scroll-bar-mode):
* lisp/simple.el (auto-fill-mode, overwrite-mode, binary-overwrite-mode)
(normal-erase-is-backspace-mode): Don't use the `eq' place.
* lisp/winner.el (winner-configuration, winner-make-point-alist)
(winner-set-conf, winner-get-point, winner-set): Don't abuse letf.
* lisp/files.el (locate-file-completion-table): Avoid list*.

Fixes: debbugs:11657