Add extern "C" layer between TCling (rtti) and rootcling (no-rtti).

core/utils/src/rootclingTCling.cxx

+// @(#)root/utils:$Id$
+// Author: Axel Naumann, 2014-04-07
+
+/*************************************************************************
+ * Copyright (C) 1995-2014, Rene Brun and Fons Rademakers.               *
+ * All rights reserved.                                                  *
+ *                                                                       *
+ * For the licensing terms see $ROOTSYS/LICENSE.                         *
+ * For the list of contributors see $ROOTSYS/README/CREDITS.             *
+ *************************************************************************/
+
+// Provides bindings to TCling (compiled with rtti) from rootcling (compiled
+// without rtti).
+
+#include "TCling.h"
+
+extern "C"
+cling::Interpreter* TCling__GetInterpreter()
+{
+   return ((TCling*)gCling)->GetInterpreter();
+}

core/utils/src/rootclingTCling.h

+// @(#)root/utils:$Id$
+// Author: Axel Naumann, 2014-04-07
+
+/*************************************************************************
+ * Copyright (C) 1995-2014, Rene Brun and Fons Rademakers.               *
+ * All rights reserved.                                                  *
+ *                                                                       *
+ * For the licensing terms see $ROOTSYS/LICENSE.                         *
+ * For the list of contributors see $ROOTSYS/README/CREDITS.             *
+ *************************************************************************/
+
+// Provides bindings to TCling (compiled with rtti) from rootcling (compiled
+// without rtti).
+
+namespace cling {
+   class Interpreter;
+}
+
+extern "C" {
+   cling::Interpreter* TCling__GetInterpreter();
+}