easy-menu subtlety

[Dan Nicolaescu <dann@ics.uci.edu>]

The last 3 lines of this code sequence in lisp/progmodes/verilog-mode.el:

    ("Move"
     ,(if (featurep 'xemacs)
          (progn 
            ["Beginning of function"            verilog-beg-of-defun t]
            ["End of function"                  verilog-end-of-defun t]
            ["Mark function"                    verilog-mark-defun t])
        ["Beginning of function"                beginning-of-defun t]
        ["End of function"                      end-of-defun t]
        ["Mark function"                        mark-defun t])

work fine on emacs-22.1 (and later), but do not work on emacs-21. 
emacs-21 throws an error when loading this file:
   Wrong type argument: listp, ["Mark function" mark-defun t]

Does anyone know how to rewrite that code so that it works both in
emacs-21 and emacs-22?  It's not obvious to me...