/usr/share/doc/gcc-6-multilib-arm-linux-gnueabihf is in gcc-6-multilib-arm-linux-gnueabihf 6.4.0-17ubuntu1cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/gcc-6-arm-linux-gnueabihf-base