Newer versions of cmake warn if CMP0075 isn't enabled. We need at least cmake version 3.12 to enable it, though, and our minimum version is currently 3.2.

3.12 also introduced the ability to set a max version in cmake_policy, which is probably a good idea. i.e. I think we'll want cmake_policy(VERSION 3.12..3.12) so that we opt into exactly the set of policies/features that were available at our minimum cmake version.

This is currently blocked on dropping support for ubuntu 18.04, which isn't EOL until 2023. https://endoflife.software/operating-systems/linux/ubuntu