Mark ConstCharStart.toString as extern too

std/cpp/ConstCharStar.hx

@@ -7,7 +7,7 @@ abstract ConstCharStar( RawConstPointer<Char> ) to(RawConstPointer<Char>)
    @:from
    static public inline function fromString(s:String) return new ConstCharStar(s);
 
-   @:to
+   @:to @:extern
    public inline function toString():String return new String(untyped this);
 
     @:to @:extern