* gnutls.c: Fix compilation warnings given fix --enable-gcc-warnings.
New macro macroexp-let2*

* emacs-lisp/macroexp.el (macroexp-let2*): New macro.

* window.el (with-temp-buffer-window)
(with-current-buffer-window, with-displayed-buffer-window):
* emacs-lisp/cl-macs.el (cl--compiler-macro-adjoin):
* emacs-lisp/cl-lib.el (substring):
* emacs-lisp/cl-extra.el (cl-getf): Use it.