/usr/share/doc/libgomp1-dbg-arm64-cross is in libgomp1-dbg-arm64-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