[SelectOpti][1/5] Setup new select-optimize pass

This is the first commit for the cmov-vs-branch optimization pass.
The goal is to develop a new profile-guided and target-independent cost/benefit analysis
for selecting conditional moves over branches when optimizing for performance.

Initially, this new pass is expected to be enabled only for instrumentation-based PGO.

RFC: https://discourse.llvm.org/t/rfc-cmov-vs-branch-optimization/6040

Reviewed By: tejohnson

Differential Revision: https://reviews.llvm.org/D120230