Add declare-function compatibility definition.

(gnus-group-mark-article-read): Declare as a function.

lisp/gnus/nnmaildir.el

@@ -61,6 +61,10 @@
    )
 ]
 
+;; For Emacs < 22.2.
+(eval-and-compile
+  (unless (fboundp 'declare-function) (defmacro declare-function (&rest r))))
+
 (eval-and-compile
   (require 'nnheader)
   (require 'gnus)
@@ -1439,6 +1443,8 @@ by nnmaildir-request-article.")
 (defun nnmaildir-active-number (gname)
   0)
 
+(declare-function gnus-group-mark-article-read "gnus-group" (group article))
+
 (defun nnmaildir-request-expire-articles (ranges &optional gname server force)
   (let ((no-force (not force))
 	(group (nnmaildir--prepare server gname))