PUBLISHED_FROM=cf49d0d345e4a7607c535f9578b8ed4160f2fccd

Note: this is only the first step; the C sources won't be built until
the second step is done.

The actual build takes about 1.3s on cloud2 which still runs the docker
containers and image layers on the very slow spinning disk. cloud3 has
docker mounted on the SSD disk; measured speedups of 20-30%

PUBLISHED_FROM=c5acef1d64ebc8dca8ed31f51685c8b3090c5767