[PATCH] Add NUMA_BUILD definition in kernel.h to avoid #ifdef CONFIG_NUMA

The NUMA_BUILD constant is always available and will be set to 1 on
NUMA_BUILDs.  That way checks valid only under CONFIG_NUMA can easily be done
without #ifdef CONFIG_NUMA

F.e.

if (NUMA_BUILD && <numa_condition>) {
...
}

[akpm: not a thing we'd normally do, but CONFIG_NUMA is special: it is
 causing ifdef explosion in core kernel, so let's see if this is a comfortable
 way in whcih to control that]

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>