Build cross toolchain using Nix

I made a Nix expression to get the cross toolchain up and running:

with import <nixpkgs> {};

let
  ocd = openocd.overrideAttrs(old: {
    name = "openocd-cardio";

    src = pkgs.fetchgit {
      url = "https://git.card10.badge.events.ccc.de/card10/openocd.git";
      rev = "90d828185cea44b29cffb40f2c8aea19282b9130";
      sha256 = "092wg19kjapv9s70b23ckd4j5i8ykk3d7mcl4h8cgl2acwcw8myr";
      fetchSubmodules = true;
    };

    nativeBuildInputs = old.nativeBuildInputs ++ [
      which
      libtool
      autoconf
      automake
    ];

    SKIP_SUBMODULE="1";

    preConfigure = ''
      ./bootstrap
    '';

  });

in pkgsCross.arm-embedded.stdenv.mkDerivation {
  name = "crossenv";
  buildInputs = [
    gdb
    ocd
  ];
}

Save this file as shell.nix and invoke nix-shell, this will then download the toolchain from the Nix binary cache and build the custom OpenOCD package.

This should also be portable to MacOS.