/usr/lib/x86_64-linux-gnu/libstdc++.so.6 is in libstdc++6 5.4.0-6ubuntu1~16.04.10.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21
/usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21