Following the discussion on D22038, this change enables the setcc to srl(ctlz) transformation on the btver2 architecture.
This optimisation is beneficial on Jaguar architecture only, where the lzcnt has a good reciprocal throughput.
Other architectures such as Intel's Haswell/Broadwell or AMD's Bulldozer/PileDriver do not benefit from it.
For this reason the change also add a "HasFastLZCNT" feature which gets enabled for Jaguar.
This patch requires D23445