these 2 derivations will be built:
  /nix/store/vz9ywndkyncdjmkam2pf7d9njqg4y3kf-harmonia-deps-3.1.0.drv
  /nix/store/c21z9zma40ma8zb0c2rvkrjz78g1pjik-harmonia-llvm-cov-3.1.0.drv