Try fixing problems from the None macro in X11 (ugh)

Samples/shell/include/x11/InputX11.h

@@ -30,6 +30,13 @@
 #define INPUTX11_H
 
 #include <X11/Xlib.h>
+
+// The None define from X.h conflicts with RmlUi code base,
+// use the constant 0L instead where necessary
+#ifdef None
+  #undef None
+#endif
+
 #include "Input.h"
 
 /**