[PATCH] add sys_unshare to syscalls.h

All architecture independent system calls should be declared
in syscalls.h, add the one that is missing.

Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>