Packet.net offer an ARMv8 server
with 96 cores for $0.50/hour. I signed up and tried building Libreoffice
to see what would happen. Debian isn't officially supported there yet, but
they offer Ubuntu, which suffices for testing the hardware.
Final build time: around 12 hours, compared to 2hr 55m on the official arm64 buildd.
Most of the Libreoffice build appeared to consist of "touch /some/file"
repeated endlessly - I have a suspicion that the I/O performance might be low
on this server (although I have no further evidence to offer for this). I
think the next thing to try is building on a tmpfs, because the server has
128GB RAM available, and it's a shame not to use it.