It looks like there's a mismatch somehow between compilers used for various
parts of the build. macports built x86_64 binaries, and some steps of ROS
are as well, but then it's trying to link as x86. The above output seems to
imply that gcc itself will output x86 code -- you can test that by writing a
simple program and then checking it with "file".
Have you made changes to your developer tools recently that might cause
something like this?