This patch adds SLQB to Kbuild. It's separated from the original patch to make
sure we don't break git bisect due to early slab changes in mainline while SLQB
was being developed.

[ penberg@cs.helsinki.fi: cut'n paste from Nick's initial patch ]
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>