Hey Guix! Very often I find myself updating systems only to get stuck on building something large like LibreOffice or Un-Googled Chromium. Usually the substitutes for these are available a few days later.
It would be nice if I could pass a flag to `guix package -u` that would disallow building in the event a substitute wasn't available. Is that `--fallback=false`? If so, that's a double-negative; is there a clearer way to represent both without acreting options? -- Katherine
