/usr/lib/gcc-cross/mips-linux-gnu/7/64/libgfortran.so is in lib64gfortran-7-dev-mips-cross 7.3.0-16ubuntu3cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc-cross/mips-linux-gnu/7/64/../../../../../mips-linux-gnu/lib64/libgfortran.so.4