tools/nolibc: move wait() and friends to sys/wait.h

This is the location regular userspace expects these definitions.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/r/20250416-nolibc-split-sys-v1-10-a069a3f1d145@linutronix.de


Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>