selftests/nolibc: report failure if no testcase passed

When nolibc-test is so broken, it doesn't even start,
don't report success.

Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/r/20240807-nolibc-llvm-v2-7-c20f2f5fc7c2@weissschuh.net


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