/usr/share/doc/libgnat-5-dbg-powerpc-cross is in libgnat-5-dbg-powerpc-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