these 2 derivations will be built:
  /nix/store/jrl8lj1w1dvzb4s1pis034m6s028c9sj-Cg-3.1_April2012_x86_64.tgz.drv
  /nix/store/s2fmxr1a4vc5kznjqsbxhg088wl7h2qv-nvidia-cg-toolkit-3.1.drv