Some news here:
We finally managed to make glxgear working. This was apparently really a
bug in llvm3.3/mesa9.2.3. Problem is, we had to recompile the whole llvm
3.5+mesa-dri 10.1 software from the git/subversion source.
Glxgears now works in archlinux, but I don't know how to recompile
easily these packages from their git/svn version using fedora.