Add declare-function compatibility definition.

(gnus-group-decoded-name): Declare as a function.

lisp/gnus/gnus.el

@@ -30,6 +30,10 @@
 
 (eval '(run-hooks 'gnus-load-hook))
 
+;; For Emacs < 22.2.
+(eval-and-compile
+  (unless (fboundp 'declare-function) (defmacro declare-function (&rest r))))
+
 (eval-when-compile (require 'cl))
 (require 'wid-edit)
 (require 'mm-util)
@@ -3736,6 +3740,8 @@ server is native)."
   "Return the prefix of the current group name."
   (< 0 (length (gnus-group-real-prefix group))))
 
+(declare-function gnus-group-decoded-name "gnus-group" (string))
+
 (defun gnus-summary-buffer-name (group)
   "Return the summary buffer name of GROUP."
   (concat "*Summary " (gnus-group-decoded-name group) "*"))