tools/nolibc: simplify stackprotector compiler flags

Now that nolibc enable stackprotector support automatically when the
compiler enables it we only have to get the -fstack-protector flags
correct.

The cc-options are structured so that -fstack-protector-all is only
enabled if -mstack-protector=guard works, as that is the only mode
supported by nolibc.

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>