[PATCH] Makefile include path ordering

The arch Makefile may override the include path order, which is used by Xen
(and UML?) to make sure include/asm-xen is searched before
include/asm-i386.

The Makefile change to 2.6.12-rc4 made the top Makefile always override the
value specified by the arch Makefile.  This trivial patch makes the Xen
kernel compile again.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>