Comment # 1 on bug 66847 from Andreas Boll

The llvm backends of r600g and the radeonsi on mesa 9.1 are only compatible
with tstellar's llvm-3.2 branch.

The llvm backends of r600g and the radeonsi on mesa 9.2 should be compatible
with the official llvm-3.3 and llvm-3.4. It's not compatible with tstellar's
llvm-3.2 branch.

So I think we should abort in configure if someone wants to build mesa 9.1 with
enabled llvm backend and llvm != 3.2.