Revert "Refactor mkFlag out of old packages"

This reverts commit 3117e0c897.

Conflicts:
	pkgs/development/libraries/wayland/default.nix
	pkgs/servers/samba/4.x.nix

pkgs/development/libraries/libinput/default.nix

@@ -9,6 +9,10 @@ assert documentationSupport -> doxygen != null && graphviz != null;
 assert eventGUISupport -> cairo != null && glib != null && gtk3 != null;
 assert testsSupport -> check != null && valgrind != null;
 
+let
+  mkFlag = optSet: flag: if optSet then "--enable-${flag}" else "--disable-${flag}";
+in
+
 with stdenv.lib;
 stdenv.mkDerivation rec {
   name = "libinput-0.15.0";
@@ -19,9 +23,9 @@ stdenv.mkDerivation rec {
   };
 
   configureFlags = [
-    (mkEnable documentationSupport "documentation" null)
-    (mkEnable eventGUISupport      "event-gui"     null)
-    (mkEnable testsSupport         "tests"         null)
+    (mkFlag documentationSupport "documentation")
+    (mkFlag eventGUISupport "event-gui")
+    (mkFlag testsSupport "tests")
   ];
 
   nativeBuildInputs = [ pkgconfig ];