Remove the lang/gcc31 port. It fails to build on several architectures
(even ones it is supposed to work on, cf. pointyhat), it fails to build
on FreeBSD 6 and 7, and lang/gcc32 is basically the same plus a single
ABI changes and many bug fixes.
It is strongly recommended to migrate to GCC 3.4 or 4.0, since only these
are still actively maintained upstream and support FreeBSD 7, for example.