/usr/mips64el-linux-gnuabi64/lib/libgfortran.so.5 is in libgfortran5-mips64el-cross 8-20180414-1ubuntu2cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/mips64el-linux-gnuabi64/lib/libgfortran.so.5.0.0