/usr/share/doc/gcc-4.8-base/Ada is in gnat-4.8-base 4.8.2-8ubuntu3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/gcc-4.8-base/../gnat-4.8-base
/usr/share/doc/gcc-4.8-base/../gnat-4.8-base