And after adding this to the commitfest, here's the first cfbot run.
The gain was due to "test_world" which shows a greater-than-2x speedup
(~4:30 -> ~2:08) from 2x CPUs. That is nice for humans who want the
answer as soon as possible, but note that the resource usage cost
might go up because of the non-parallel parts now wasting more idle
CPUs: git clone, meson configure etc (as they do on every platform).
https://cirrus-ci.com/build/6060109692928000
