Build Pyre binaries using older Linux versions

[stroxler]

The released Linux Pyre binaries on PyPI are currently built from this codebase on machines that generally run very recent versions of Linux.

This has caused problems because the glibc Pyre's build picks up is very new, which can lead to failures like the one reported in #860 when users run against an older Linux.

A few fixes are possible, like trying to statically link some other C library, but the most standard solution is to just build in a container that has a reasonably old glibc so that the binary should "just work" for anyone running a not-ancient system.

To do this, we probably want to move our release builds to either github actions or CircleCI. In the process it would be a good idea to start running the full OCaml test suite in github CI (at the moment we only run it internally).