/usr/share/doc/gcc-6-sparc64-linux-gnu is in gcc-6-sparc64-linux-gnu 6.4.0-17ubuntu1cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/gcc-6-sparc64-linux-gnu-base
/usr/share/doc/gcc-6-sparc64-linux-gnu-base