conftest.c:12:12: error: unknown type name 'barfbarf'
That is an error message, but it is an intentional error message. That's how configure scripts work. They do things, some of which generate errors, and depending on what happened the configure script learns things about your system. If you look a couple lines above that error message in the config.log, you'll see it's part of the test "checking whether the compiler is clang" and below the error and the program that generated it, "result: yes". So the test successfully identified that your compiler is clang. So far so good.
Looking toward the end of the config.log, I see the real problem was:
configure:17526: error: xwidgets requested but WebKitGTK+ or WebKit framework not found.
As to why that happened, I'll leave that to the port's maintainers, to whom I'm assigning the ticket.
