/usr/lib/ocaml/apron/polka.a is in libapron-ocaml-dev 0.9.10-6.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ocaml/apron/polkaMPQ.a
/usr/lib/ocaml/apron/polkaMPQ.a