anchor.diff:  , withGTK2 ? false, gtk2-x11 ? null
   , withGTK3 ? true, gtk3-x11 ? null, gsettings-desktop-schemas ? null
   , withXwidgets ? false, webkitgtk ? null, wrapGAppsHook ? null, glib-networking ? null
  +, withMotif ? false, motif ? null
   , withCsrc ? true
   , srcRepo ? false, autoreconfHook ? null, texinfo ? null
   , siteStart ? ./site-start.el
  
positive.code:     ++ lib.optionals (stdenv.isLinux && withX) [ m17n_lib libotf ]
      ++ lib.optional (withX && withGTK2) gtk2-x11
      ++ lib.optionals (withX && withGTK3) [ gtk3-x11 gsettings-desktop-schemas ]
      ++ lib.optionals (withX && withXwidgets) [ webkitgtk glib-networking ]
      ++ lib.optionals withNS [ AppKit GSS ImageIO ]
      ++ lib.optionals nativeComp [ libgccjit ]
  
negative.code: , toolkit ? (
    if withGTK2 then "gtk2"
    else if withGTK3 then "gtk3"
    else if withMotif then "motif"
    else "lucid")
  }:
  
  