these 2 derivations will be built:
  /nix/store/y2hwgwq4c2sr61kbigg83w06bs15p4vm-nix-bindings-expr-sys-deps-0.2.1.drv
  /nix/store/x20g96czn3hnsibqbibyfb746ph20zv4-nix-bindings-expr-sys-0.2.1.drv