anchor.diff:  
     installPhase =
       ''
  -      set -u
  -
         mkdir -p $out/bin $out/nix-support
   
         wrap() {
           local dst="$1"
           local wrapper="$2"
           export prog="$3"
  -        set +u
           substituteAll "$wrapper" "$out/bin/$dst"
  -        set -u
           chmod +x "$out/bin/$dst"
         }
       ''
  
positive.code:         [[ -e "$underlying" ]] || continue
          wrap ${targetPrefix}$variant ${./ld-wrapper.sh} $underlying
        done
  
        set +u
      '';
  
    emulation = let
  
negative.code:     ''
  
      + ''
        substituteAll ${./add-flags.sh} $out/nix-support/add-flags.sh
        substituteAll ${./add-hardening.sh} $out/nix-support/add-hardening.sh
        substituteAll ${../wrapper-common/utils.bash} $out/nix-support/utils.bash
  