Add shell.nix for easier fuzzing

Author: killercup

shell.nix

@@ -0,0 +1,20 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+let
+  moz_overlay = import (builtins.fetchTarball "https://github.com/mozilla/nixpkgs-mozilla/archive/master.tar.gz");
+  nixpkgs = import <nixpkgs> { overlays = [ moz_overlay ]; };
+  custom = import (builtins.fetchTarball {
+    name = "killercup-nixpkgs";
+    url = "https://github.com/killercup/nixpkgs/archive/cargo-fuzz-0.5.4.tar.gz";
+  }) {};
+in pkgs.mkShell {
+  buildInputs = with pkgs; [
+    git
+    (nixpkgs.rustChannelOf { date = "2019-10-23"; channel = "nightly"; }).rust
+    custom.pkgs.cargo-fuzz
+  ];
+
+  RUSTFLAGS="-C link-arg=-fuse-ld=gold";
+  RUST_BACKTRACE = 1;
+}
+