hack for C++11 ambiguity

Index: v2cc/v2cc-decl.cc
--- v2cc/v2cc-decl.cc.orig
+++ v2cc/v2cc-decl.cc
@@ -13,6 +13,7 @@
 #include "mapping.h"
 #include "v2cc-util.h"
 
+#define to_string ::to_string
 
 void test (RegionStack &rstack)
 {