Define an add_const utility function

This is useful in particular when we want to force the const version of
a method to be called.
For exprt there can be differences in performance between const and
non-const.

Author: romainbrenguier

src/util/add_const.h

@@ -0,0 +1,19 @@
+/*******************************************************************\
+
+Module: Util
+
+Author: Romain Brenguier, [email protected]
+
+\*******************************************************************/
+
+#ifndef CPROVER_UTIL_ADD_CONST_H
+#define CPROVER_UTIL_ADD_CONST_H
+
+/// Return a reference to the same object but ensures the type is const
+template <typename T>
+const T &add_const(T &value)
+{
+  return static_cast<const T &>(value);
+}
+
+#endif // CPROVER_UTIL_ADD_CONST_H