anchor.diff:  
     defaultBuildInputs = extraBuildInputs;
   
  +  stdenv = (stdenv-overridable argsStdenv);
  +
     # The stdenv that we are producing.
  -  stdenv =
  +  in
       derivation (
       lib.optionalAttrs (allowedRequisites != null) {
         allowedRequisites = allowedRequisites
  
positive.code:     # "lift" packages like curl from the final stdenv for Linux to
      # all-packages.nix for that platform (meaning that it has a line
      # like curl = if stdenv ? curl then stdenv.curl else ...).
      // extraAttrs;
  
  in stdenv)
  
negative.code: let lib = import ../../../lib; stdenv-overridable = lib.makeOverridable (
  
  argsStdenv@{ name ? "stdenv", preHook ? "", initialPath
  
  , # If we don't have a C compiler, we might either have `cc = null` or `cc =
    # throw ...`, but if we do have a C compiler we should definiely have `cc !=
  