tools/nolibc: add support for prctl()

It will be used to disable core dumps from the child spawned to validate
the stack protector functionality.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>