Change ID prefix from $$ to something that passes better in the resul…

…ting cmake dep file.

src/lib/option.cpp

@@ -121,7 +121,7 @@ vector<string> Option::DynamicMethodPostfixes;
 vector<string> Option::DynamicClassPrefixes;
 vector<string> Option::DynamicClassPostfixes;
 set<string> Option::DynamicInvokeFunctions;
-string Option::IdPrefix = "$$";
+string Option::IdPrefix = "_DupId";
 string Option::LambdaPrefix = "df_";
 string Option::Tab = "  ";