anchor.diff:  assert documentationSupport ->
     doxygen != null
     && graphviz != null;
  -assert eventGUISupport ->
  +assert debugGUISupport ->
     cairo != null
     && glib != null
     && gtk3 != null;
  
positive.code: 
    configureFlags = [
      "--${boolEn documentationSupport}-documentation"
      "--${boolEn eventGUISupport}-event-gui"
      "--${boolEn testsSupport}-tests"
    ];
  
  
negative.code:     libwacom
      mtdev
      systemd_lib
    ] ++ optionals debugGUISupport [
      cairo
      glib
      gtk3
  