Required module `Bigarray' is unavailable

I'm trying to find out why [capnp master's tests](https://ci.ocamllabs.io/github/capnproto/capnp-ocaml/commit/4aaf51db3fa24c363785c9a7cf4d096ceb55d09c) don't work on OCaml 4.07, and the ```Required module `Bigarray' is unavailable``` error seems to be connected to `Base_quickcheck`. I thought it would be good to enable CI on this repository to see if it shows up here too.

If you'd like to enable ocaml-ci here, go to https://github.com/apps/ocaml-ci and add the GitHub app to this organisation (making sure to limit it to just the `base` repository when prompted). I've already added `janestreet` to the whitelist, so no other configuration should be needed.

Start by reviewing the linked capnp master's CI results and the Base_quickcheck failure on OCaml 4.07. Follow the ocaml-ci GitHub App setup instructions in the issue, limiting access to the base repository, and confirm that CI runs here and exposes the compatibility failure.

Written by the indexing model from the issue text.