tools/nolibc: x86_64: disable stack protector for _start

tools/nolibc: x86_64: disable stack protector for _start

This was forgotten in the original submission.

It is unknown why it worked for x86_64 on some compiler without this
attribute.

Reported-by: Willy Tarreau <w@1wt.eu>
Closes: https://lore.kernel.org/lkml/20230520133237.GA27501@1wt.eu/
Fixes: 0d8c461adbc4 ("tools/nolibc: x86_64: add stackprotector support")
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>