selftests/nolibc: allow run nolibc-test locally

It is able to run nolibc-test directly without qemu-user when the target
machine is the same as the host machine.

Sometimes, the result running locally may help a lot when the qemu-user
package is too old.

When the target machine differs from the host machine, it is also able
to run nolibc-test directly with qemu-user-static + binfmt_misc.

Link: https://lore.kernel.org/lkml/ZKutZwIOfy5MqedG@1wt.eu/


Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>