PGO will probably come to LLVM soon, for what it's worth. They added branch probability and basic block frequency support in 3.0 with an eye towards it, anyway.
Great, yes there's been propositions made towards it for quite some time but no actual code so I was almost thinking it wouldn't happen, here's hoping it will happen now. Every other major compiler I can think of has it, GCC, ICC, Open64, MSVC, and the optimization often has a great impact on performance dependant code.