This fixes the error:

In file included from mutt_menu.h:23,
                 from addrbook.c:20:
keymap.h:83: error: array type has incomplete element type

diff -dur mutt-1.4.2.1/keymap.c src.mutt.1129843324.3091.4058436413/mutt-1.4.2.1/keymap.c
--- mutt-1.4.2.1/keymap.c	2001-10-16 16:29:27.000000000 +0200
+++ src.mutt.1129843324.3091.4058436413/mutt-1.4.2.1/keymap.c	2005-10-20 23:45:08.000000000 +0200
@@ -28,7 +28,7 @@
 
 #include "functions.h"
 
-struct mapping_t Menus[] = {
+struct mapping_t *Menus = {
  { "alias",	MENU_ALIAS },
  { "attach",	MENU_ATTACH },
  { "browser",	MENU_FOLDER },
diff -dur mutt-1.4.2.1/keymap.h src.mutt.1129843324.3091.4058436413/mutt-1.4.2.1/keymap.h
--- mutt-1.4.2.1/keymap.h	2001-09-11 13:20:34.000000000 +0200
+++ src.mutt.1129843324.3091.4058436413/mutt-1.4.2.1/keymap.h	2005-10-20 23:44:07.000000000 +0200
@@ -80,7 +80,7 @@
 /* dokey() records the last real key pressed  */
 extern int LastKey;
 
-extern struct mapping_t Menus[];
+extern struct mapping_t *Menus;
 
 struct binding_t
 {