Linking issue in utility functions

[yuhc]

Some functions and variables like guestlib_tf_opt_init and fatbin_handle_list are defined and used for utility functions. Those utility functions are used only in either guestlib or worker, but have to be compiled into both for now. Currently, we add dummy definitions for such functions and variables in guestlib or worker to suppress the compiler error. But we should find a better way for this in the end.