I have compiled a working 64bit radiant from SVN (rev 166) with gcc 4.1.2. You can find it here:
gtkradiant-svn-166-x86_64.tar.bz2The tarball contains all the radiant binaries, plugins and the tremulous pack. It assumes tremulous is in /opt/games/tremulous. If your tremulous is installed somewhere else, you'll have to edit the file games/tremulous.game and change the line that says
enginepath_linux="/opt/games/tremulous/"
It works for me, your mileage may vary.