nix-exec broken on master, fine on release-16.09

[jpierre03]

Issue description

Nix-exec package can't be built on master branch.
Broken for i686 https://hydra.nixos.org/job/nixos/trunk-combined/nixpkgs.nix-exec.i686-linux/all and x86_64 https://hydra.nixos.org/job/nixos/trunk-combined/nixpkgs.nix-exec.x86_64-linux/all since 2016-12-11

It seems related to a nix langage API change, commit NixOS/nix@cb5e725.

https://hydra.nixos.org/build/44683739/nixlog/1

/nix/store/add4869c9wrvg611l2py4j3hhb6wd5vp-nix-1.12pre4911_b30d1e7-dev/include/nix/util.hh:172:10: error: 'void nix::AutoCloseFD::close()' is private
     void close();
          ^
src/fetchgit.cc:99:27: error: within this context
       pipe.readSide.close();

cc @shlevy

Technical details

• System: NixOS official hydra & local build with nix-shell -p nox --run "nox-review wip"
• Nixpkgs version: 17.03pre99759.f66d782

[jpierre03]

@shlevy thanks.