/usr/share/doc/gcc-7-plugin-dev-riscv64-linux-gnu is in gcc-7-plugin-dev-riscv64-linux-gnu 7.3.0-16ubuntu3cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/gcc-7-riscv64-linux-gnu-base