/usr/share/doc/libn32gcc-7-dev-mips64-cross is in libn32gcc-7-dev-mips64-cross 7.3.0-16ubuntu3cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/gcc-7-cross-base-ports
/usr/share/doc/gcc-7-cross-base-ports