Rebase: Merge BOLT codebase in monorepo

Summary:
This commit is the first step in rebasing all of BOLT
history in the LLVM monorepo. It also solves trivial build issues
by updating BOLT codebase to use current LLVM. There is still work
left in rebasing some BOLT features and in making sure everything
is working as intended.

History has been rewritten to put BOLT in the /bolt folder, as
opposed to /tools/llvm-bolt.

(cherry picked from FBD33289252)