use identifier representation of symbols for back reference comparison

Author: rainers

src/dmangle.d

@@ -209,12 +209,13 @@ public:
     {
         version(useBackref)
         {
-            if (auto p = cast(void*)s in symbols)
+            Identifier id = s.getIdent();
+            if (auto p = cast(void*)id in symbols)
             {
                 buf.printf("%d$", cast(int)*p);
                 return true;
             }
-            symbols[cast(void*)s] = symbols.length;
+            symbols[cast(void*)id] = symbols.length;
         }
         return false;
     }