Fix failing tests and add Guix infrastructure

Hello,

I'm interested in packaging industria for Guix, and its only runtime dependency not yet packaged for Guix is this library. In writing a package for local testing purposes, I ran across some build issues and decided it would be best to submit those changes upstream. I've taken the liberty of including the guix.scm file I wrote in the process as well. The guix.scm file, if you're unfamiliar, can be used with the -f flag of various Guix commands like build, install, and shell to make the package available for various purposes. Adding -D as in -Df instead exposes the native-inputs.

The issue I ran into was that the test-runner-get function was being called outside the context of an active test runner. To resolve this, I simply separated the tracking of failed tests, which is done inside the context of an active test runner, and the reporting of the failed tests to the operating system, which is done last in the file.