/usr/share/doc/gcc-4.6-base/Ada is in gnat-4.6-base 4.6.4-0ubuntu5.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/gcc-4.6-base/../gnat-4.6-base
/usr/share/doc/gcc-4.6-base/../gnat-4.6-base