Fix some dependency problems that cause unnecessary recompiles.

Fix some dependency problems that cause unnecessary recompiles.

Problem reported by RMS in
<http://lists.gnu.org/archive/html/emacs-devel/2013-11/msg00421.html>.
* configure.ac (OLDXMENU_TARGET, OLDXMENU, LIBXMENU, OLDXMENU_DEPS):
Remove.
(LIBXMENU_DIR, LIBXMENU_BASE): New vars.
* src/Makefile.in (OLDXMENU_TARGET, OLDXMENU, OLDXMENU_DEPS)
(really-lwlib, really-oldXMenu, stamp-oldxmenu)
(../src/$(OLDXMENU), $(OLDXMENU)): Remove.
(LIBXMENU_DIR, LIBXMENU_BASE): New macros.
(LIBXMENU): Use them.
(temacs$(EXEEXT)): Depend on $(LIBXMENU), not stamp-oldxmenu.
($(lwlibdir)/liblw.a, $(oldXMenudir)/libXMenu11.a, FORCE): New targets.
(boostrap-clean): No need to remove stamp-oldxmenu.