Improve bitness detection in the configure script (use the fact that all
64-bit architectures supported by FreeBSD have that ``64'' suffix in the
machine processor architecture reported by ``uname -p'') and tentatively
unbreak the port, well, everywhere. While here, remove outdated and now
useless, no-op fixups for the configure script.

Tested on: i386, amd64, powerpc, sparc64