Comment # 74 on bug 81644 from Michel Dänzer

(In reply to comment #73)
> Could it be I'm using LLVM 3.6 [...]

Yes, only released versions of LLVM can be supported by released versions of
Mesa. Even LLVM 3.5 is only being released now, so you might need LLVM 3.4(.y)
for Mesa 10.1.