Hi, Bernardo
Fedora has a patch for LLVM 2.2 release with gcc 4.3 here:
http://cvs.fedora.redhat.com/viewcvs/rpms/llvm/devel/llvm-2.2-gcc43.patch
Just drop it in the llvm-2.2 directory and execute
$ patch -p1 < llvm-2.2-gcc43.patch
It should build cleanly afterwards.