feat(third_party): Add Google's farmhash library

third_party/farmhash/default.nix

@@ -0,0 +1,13 @@
+# Google's farmhash family of hash functions
+{ pkgs, ... }:
+
+pkgs.stdenv.mkDerivation {
+  name = "farmhash";
+
+  src = pkgs.fetchFromGitHub {
+    owner = "google";
+    repo = "farmhash";
+    rev = "0d859a811870d10f53a594927d0d0b97573ad06d";
+    sha256 = "1w2583m5289hby0r91gds5yia6l8qpmzkl5b9bv58g5gacfj2h17";
+  };
+}