/usr/mips-linux-gnu/lib64/debug/libstdc++.so is in lib64stdc++6-5-dbg-mips-cross 5.5.0-12ubuntu1cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/mips-linux-gnu/lib64/debug/libstdc++.so.6.0.21