x86: fix kernel rebuild due to vsyscall fallout

Fix rebuild of kernel when there is no changes.
This happened for i386.
Using make V=2 hinted that the output files were
not assigned to targets - fixed by this patch.

Reported by: Boaz Harrosh <bharrosh@panasas.com>

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>