x/build/cmd/racebuild: migrate to LUCI

[cherrymui]

Currently the racebuild command still uses legacy gomotes, some of which may no longer exist now. We should migrate it to LUCI, for builders that already migrated.

One tricky thing is that it currently depends on it running as root and being able to install commands, like apt-get or yum install. But this is not possible on the LUCI builders. It mostly wants to install git, g++, and unzip. Looks like we already have the first two installed. So we may need to install unzip on the builders, or make it available through some other mechanism.

cc @golang/release @mknyszek

[abner-chenc]

Gentle ping.

[gopherbot]

Change https://go.dev/cl/672097 mentions this issue: cmd/racebuild: update gomote names and remove commands that need root

[gopherbot]

Change https://go.dev/cl/672096 mentions this issue: env: install unzip in Linux images

[mknyszek]

I believe I got it working on most platforms, especially the first class ones, but didn't check every single platform (some of them are broken for other reasons). I'll leave this closed for now but double-check.

[mknyszek]

Ah, OK. Windows is still broken because it doesn't have gcc installed, or at least not available in the way it's needed.