crossgcc won't build on openSUSE 12.1 x86_64 because the gmp libraries
end up in xgcc/lib64/ (as designed) but mpfr expects them to be in
xgcc/lib/ (why?). Workaround is to add a symlink xgcc/lib -> xgcc/lib64 .
autoconf is claimed to be needed to build binutils (at least according
to buildgcc), but buildgcc ignores a missing autoconf and proceeds
anyway. That's not a problem, binutils builds just fine.
I wanted to give other openSUSE 12.1 users a heads-up and make the
solution searchable via the mailing list archive.