list: Avoid using X types

In particular, Bool.  This is not an ABI break:

/usr/include/X11/Xdefs.h:typedef int Bool;

Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Adam Jackson <ajax@redhat.com>

include/list.h

@@ -213,7 +213,7 @@ xorg_list_del(struct xorg_list *entry)
  *
  * @return True if the list contains one or more elements or False otherwise.
  */
-static inline Bool
+static inline int
 xorg_list_is_empty(struct xorg_list *head)
 {
     return head->next == head;