Show build trace in buildbot

[eljamm]

It would be nice if the builds show the trace, since it's useful to get as much information as possible, especially if the issue can't be reproduced on a contributor's system.

Example: Build succeeds for x86_64-linux but fails for aarch64-linux.

[Erethon]

For the record, I created nix-community/buildbot-nix#438 upstream to handle this. Tested on https://buildbot.ngi.nixos.org/#/builders/175/builds/1800 and seems to work.

Will leave this issue open until we actually implement this in makemake for good (either by the upstream PR being merged or us patching it locally).