/usr/lib/x86_64-linux-gnu/debug/libstdc++.so.6 is in libstdc++6-6-dbg 6.4.0-17ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/debug/libstdc++.so.6.0.22
/usr/lib/x86_64-linux-gnu/debug/libstdc++.so.6.0.22