Cirrus: Build/upload Nightly binaries with gox

[JeremyRand]

It would be desirable to build Nightly binaries with gox (for all supported architectures) and upload them as Cirrus artifacts. The ncdns Cirrus config should be a good pointer on how to do this.

[JeremyRand]

@robertmin1 Is anything currently blocking this? (If we can only build Nightlies with Go Modules disabled, that's still better than the status quo.)

[robertmin1]

I have been working on it, but I feel a bit confused when I examine comparable approaches. I will raise the issue incase I don't figure it out