these 2 derivations will be built:
  /nix/store/0vnqzk4mb4x0xk4lh9c018sy83sggiwy-szip-2.1.1.tar.gz.drv
  /nix/store/wq9pgq1y9nd0imwds29qgi8nqc1p8kga-szip-2.1.1.drv