hurd: Also make it possible to call strlen very early

strlen, which is another ifunc-selected function, is invoked during
early static executable startup if the argv arrives from the exec
server. Make it not crash.

Checked on x86_64-gnu: statically linked executables launched after the
exec server is up now start up successfully.

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
Message-Id: <20230517191436.73636-10-bugaevc@gmail.com>