[PATCH] Link error when futexes are disabled on 64bit architectures

If futexes are disabled we fail to link on ppc64.

Signed-off-by: Anton Blanchard <anton@samba.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>