Fix x64 build failing after r21366.

runtime/vm/code_generator.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/code_generator.h"
 
 #include "vm/assembler.h"
 #include "vm/ast.h"
 #include "vm/bigint_operations.h"
 #include "vm/code_patcher.h"
@@ skipping 1032 matching lines @@
         Exceptions::PropagateError(error);
       }
     }
     ASSERT(target.HasCode());
     instructions = Code::Handle(target.CurrentCode()).instructions();
   }
   arguments.SetReturn(instructions);
   if (instructions.IsNull()) return;
 
   cache.EnsureCapacity();
-  const Smi& class_id = Smi::Handle(Smi::New(is_null ? kNullCid : cls.id()));
+  const Smi& class_id = Smi::Handle(Smi::New(
+      is_null ? static_cast<intptr_t>(kNullCid) : cls.id()));
   cache.Insert(class_id, target);
   return;
 }
 
 
 // Updates IC data for two arguments. Used by the equality operation when
 // the control flow bypasses regular inline cache (null arguments).
 //   Arg0: Receiver object.
 //   Arg1: Argument after receiver.
 //   Arg2: Target's name.
@@ skipping 662 matching lines @@
 //   Arg1: Value that is being stored.
 DEFINE_RUNTIME_ENTRY(UpdateFieldCid, 2) {
   ASSERT(arguments.ArgCount() == kUpdateFieldCidRuntimeEntry.argument_count());
   const Field& field = Field::CheckedHandle(arguments.ArgAt(0));
   const Object& value = Object::Handle(arguments.ArgAt(1));
 
   field.UpdateCid(Class::Handle(value.clazz()).id());
 }
 
 }  // namespace dart