Merge BOLT into LLVM monorepo

Details of the merge are available at llvm-dev.

Mailing-list: https://lists.llvm.org/pipermail/llvm-dev/2022-January/154638.html

 [llvm-dev] Preparing BOLT for LLVM monorepo

Co-authored-by: Rafael Auler <rafaelauler@fb.com>