Fixed GCC build (32-bit).

Engine/Container/Hash.h

@@ -22,6 +22,8 @@
 
 #pragma once
 
+#include <cstddef>
+
 namespace Urho3D
 {
 

Engine/Container/Ptr.h

@@ -25,6 +25,7 @@
 #include "RefCounted.h"
 
 #include <cassert>
+#include <cstddef>
 
 namespace Urho3D
 {