Move wrapNonNixProgram to utils module

Define the wrapNonNixProgram in my Nix utils module.

utils/default.nix

@@ -0,0 +1,14 @@
+{ pkgs, ... }:
+
+# Using this as a library to define some common utility functions that I often
+# reach for.
+{
+  # A unary function that returns its argument.
+  identity = x: x;
+
+  # Create a derivation that creates an executable shell script named `as` that
+  # calls the program located at `path`, forwarding all of the arguments.
+  wrapNonNixProgram = { path, as }: pkgs.writeShellScriptBin as ''
+    exec ${path} "$@"
+  '';
+}