COMMON: Add type traits to common library

Type traits allow conditional selection and manipulation of types
during compilation.

common/type-traits.h

@@ -0,0 +1,34 @@
+/* ScummVM - Graphic Adventure Engine
+ *
+ * ScummVM is the legal property of its developers, whose names
+ * are too numerous to list here. Please refer to the COPYRIGHT
+ * file distributed with this source distribution.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ */
+
+#ifndef COMMON_TYPE_TRAITS_H
+#define COMMON_TYPE_TRAITS_H
+
+namespace Common {
+	template <bool b, class T, class U> struct Conditional { typedef T type; };
+	template <class T, class U> struct Conditional<false, T, U> { typedef U type; };
+	template <typename T> struct RemoveConst { typedef T type; };
+	template <typename T> struct RemoveConst<const T> { typedef T type; };
+	template <typename T> struct AddConst { typedef const T type; };
+} // End of namespace Common
+
+#endif