/usr/share/doc/lib64gfortran4-dbg-mipsel-cross is in lib64gfortran4-dbg-mipsel-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