Add stdenvNoCC

This is a standard environment that doesn't contain a C/C++
compiler. This is mostly to prevent trivial builders like runCommand
and substituteAll from pulling in gcc for simple configuration changes
on NixOS.

nixos/modules/system/etc/etc.nix

@@ -8,7 +8,7 @@ let
 
   etc' = filter (f: f.enable) (attrValues config.environment.etc);
 
-  etc = pkgs.stdenv.mkDerivation {
+  etc = pkgs.stdenvNoCC.mkDerivation {
     name = "etc";
 
     builder = ./make-etc.sh;