Looks like the first error in the log is actually:
:info:build ../../../../../3rdparty/asio/include/asio/detail/string_view.hpp:31:12: error: no member named 'experimental' in namespace 'std'
:info:build using std::experimental::basic_string_view;
:info:build ~~~~~^
:info:build ../../../../../3rdparty/asio/include/asio/detail/string_view.hpp:32:12: error: no member named 'experimental' in namespace 'std'
:info:build using std::experimental::string_view;
:info:build ~~~~~^
In any case, this sounds like a problem that is not specific to MacPorts. I will update the port to the latest version, 0.216. If the problem persists with that version, please report the problem to the developers; they may need to update their bundled asio library.