All commands should be performed in the chroot.
First, login to Goma:
$ goma_auth login
You'll be prompted to accept an agreement, and copy a URL into your browser for login. Be sure to use your @google.com account.
The login info should persist across reboots, so you'll only need to do this step once (or rarely, if you get logged out).
Start Goma's compiler_proxy daemon. It will run in the background.
$ goma_ctl ensure_start
You'll need to do this each time you start your machine.
Run zmake as you normally do, and just add the --goma flag. For example:
$ zmake --goma testall
jrosenth@ observed on a ThinkStation P920 that a clean testall with --goma takes only 1 minute 55 seconds, versus 8 minutes and 20 seconds without, so it's worth setting up!
The Makefile doesn't yet support Goma, but this is planned for the future. b/214323409 tracks the progress.