/usr/lib/gcc-cross/mips64el-linux-gnuabi64/6/n32/libstdc++.so is in libn32stdc++-6-dev-mips64el-cross 6.3.0-18cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc-cross/mips64el-linux-gnuabi64/6/n32/../../../../../mips64el-linux-gnuabi64/lib32/libstdc++.so.6