/usr/lib/gcc/x86_64-linux-gnu/8/x32/libstdc++.so is in libx32stdc++-8-dev 8-20180414-1ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc/x86_64-linux-gnu/8/x32/../../../../../libx32/libstdc++.so.6