fakeroot not supported on x86_64-darwin

[carnott-snap]

Issue description

fakeroot does not appear to be supported on macOS; this is possible via homebrew, and works with no issue, so it does not appear to be a technical limitation. I am not familiar enough with Nix to port over the homebrew packaging, but was planning on taking a stab if this issue does not get traction.

Steps to reproduce

$ nix-shell -p fakeroot

or

$ nix-env -i fakeroot

Technical details

error: Package ‘fakeroot-1.20.2’ in ‘/nix/store/.../nixpkgs/pkgs/tools/system/fakeroot/default.nix:22’ is not supported on ‘x86_64-darwin’, refusing to evaluate.

and

error: selector ‘fakeroot’ matches no derivations

• System: macOS Sierra 10.12.3 (16D32)
• Nix version: nix-env (Nix) 1.11.5
• Nixpkgs version: 17.03pre98135.3ac20e9