Hm... Are you sure that you started from a completely fresh source tree?
The problem is that the GCC version distributed with FreeBSD 5.3 doesn't like it if either _GLIBCXX_DEBUG or _GLIBCXX_DEBUG_PEDANTIC are defined. They are defined by default, but not if --disable-debug was passed to ./configure. Maybe there are some leftovers from a previous ./configure run, so try it again with a completely fresh source tree.
EDIT: While we are at it, could you please post a longer error message if the problem occurs again? I mean, not only the actual error message itself, but also the last gcc/g++ call above it.