(grep-mode): Use normal autoload cookie.

lisp/progmodes/grep.el

@@ -500,7 +500,17 @@ temporarily highlight in visited source lines."
 			 command-args)
 		       'grep-mode nil highlight-regexp)))
 
-;;;###autoload (autoload 'grep-mode "grep" nil t)
+;;; This doesn't work:
+;;;      ###autoload (autoload 'grep-mode "grep" nil t)
+;;; The ostensibly correct result is nonetheless opaque to the accounting
+;;; done in `generate-file-autoloads'; in loaddefs.el, the generated elisp is
+;;; correct but the generated header comment for grep.el lacks `grep-mode'.
+;;; This approach also doesn't help other users of `define-compilation-mode'
+;;; who wish to autoload.
+;;;
+;;; Better to extend autoload.el to grok `define-compilation-mode'.
+
+;;;###autoload
 (define-compilation-mode grep-mode "Grep"
   "Sets `grep-last-buffer' and `compilation-window-height'."
   (setq grep-last-buffer (current-buffer))