x/build: add LUCI illumos-amd64 builder

[dmitshur]

There currently isn't a LUCI builder that tests the illumos/amd64 port (other than the misc-compile builder, which tests only that the port compiles). This is the tracking issue for it.

The next steps that a builder owner will need to follow to make progress here are documented https://go.dev/wiki/DashboardBuilders#luci-builders.

[jclulow]

G'day! I am creating the new builder with hostname illumos-amd64-jclulow.

The CSR is attached: illumos-amd64-jclulow.csr.txt

Please, Mr. Music, will you play?

[dmitshur]

Thank you for starting to work on this builder. Here's the certificate:
illumos-amd64-jclulow-1715889249.cert.txt.

Edit: I'll also note that if the previous coordinator-based builder starts to get in the way of you bringing up the new LUCI builder, you should feel free to stop the previous builder and focus on the new one. It's certainly fine to keep the old one running if it doesn't get in the way. Thanks.

[jclulow]

I put the new one in a new VM, so they don't interact. The host is definitely getting LUCI tokens, and the swarm thing is definitely doing something inscrutable and then rebooting the instance every now and again.

I had a peek in some logs, and I think it's a bit confused about the platform: it says "solaris-amd64" in a bunch of log messages, which is obviously not quite right, it should be "illumos-amd64" presumably.

Please let me know what to do next!