Thanks for the reply.
It is too difficult to debug these errors for me, especially when I am not a c++ coder.
I did manage to get rid of "fc::raw::unpack" error by removing the ... from flat_fwd.hpp's line 19 and 20, to make the template parameters explicit, I am not sure if it is a correct change though. Still trying to figure out the other error.

change from:

      template<typename Stream, typename K, typename... V>
      void unpack( Stream& s, flat_map<K,V...>& value ) ;

to:

      template<typename Stream, typename K, typename V> 
      void unpack( Stream& s, flat_map<K,V>& value ) ;