Offer precompiled binaries for download

[alexwlchan]

Having to download the Xcode Command Line Tools is a non-trivial bar to usage. It'd be nice if I could offer precompiled binaries for people to download.

I wonder if I could do this in GitHub Actions?

[alexwlchan]

Precompiled binaries are also a heck of a lot faster!

[alexwlchan]

Okay I got it working somewhat, but it seems to have built Apple Silicon images for both builds!

Which kinda makes sense, there was nothing to distinguish them. Let's see if my next build gets me an Intel build.

[alexwlchan]

Okay now it works and creates the correct binary, but they aren't notarised. So that's the next step!