/usr/lib/x86_64-linux-gnu/libexpat.so is in libexpat1-dev 2.2.0-2+deb9u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /lib/x86_64-linux-gnu/libexpat.so.1.6.2
/lib/x86_64-linux-gnu/libexpat.so.1.6.2