The log says the error is:
:info:build ld: in '/opt/local/lib/libxml2.2.dylib', file was built for x86_64 which is not the architecture being linked (i386): /opt/local/lib/libxml2.2.dylib for architecture i386
:info:build clang: error: linker command failed with exit code 1 (use -v to see invocation)
You're building gobject-introspection universal, but for some reason your libxml2 library is not universal. MacPorts thinks your installed libxml2 port is already universal; you can verify this by running "port -v installed libxml2"—the output should include the string "+universal". If it were not so, MacPorts would have automatically rebuilt your libxml2 port universal for you. But the error message says it isn't universal, so it seems that something has overwritten your universal libxml2 library with a non-universal one, behind MacPorts' back. How did that happen? Did you run a third-party installer that overwrote some of your MacPorts files? (Third-party installers should not do that, but some do; if you can remember which installer it was, then you can report the problem to the distributors of that installer.)
If your libxml2 library was overwritten, who knows how many other files were overwritten as well. To fix the problem, the cleanest solution, least likely to result in further problems down the road, is to uninstall all ports, and MacPorts itself (including deleting the /opt/local directory, after first saving anything important therein), then reinstalling MacPorts and the ports you want.
