smp_call_function_single() needs to be visible in non-SMP builds, to fix:

arch/x86_64/kernel/vsyscall.c:283: warning: implicit declaration of function 'smp_call_function_single'
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>