syscalls: Prepare syscalls and bits for (mostly) setting creds

These are setXXXid, capset and various bits for prctl and caps machinery.
The thing is that the caps API is not yet fully in glibc so we have to
declare some bits even for core code, not just for restorer/parasite.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>