tools/nolibc: add stdbool.h header

stdbool.h is very simple.
Provide an implementation for the user convenience.

Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/r/20240725-nolibc-stdbool-v1-1-a6ee2c80bcde@weissschuh.net


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