/usr/s390x-linux-gnu/lib/libstdc++.so.6 is in libstdc++6-s390x-cross 6.3.0-18cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/s390x-linux-gnu/lib/libstdc++.so.6.0.22
/usr/s390x-linux-gnu/lib/libstdc++.so.6.0.22