/usr/share/doc/libgnatvsn5-dbg-armhf-cross is in libgnatvsn5-dbg-armhf-cross 5.3.1-14ubuntu2cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/gcc-5-cross-base
/usr/share/doc/gcc-5-cross-base