[llvm] [RFC][BOLT] Add a new parallel DWARF processing(2/2) (PR #197859)

[Alexander Yermolovich via llvm-commits]

ayermolo wrote:

> cc @ayermolo , I've rebased the PR. Please review it when you have a chance?

Left some comments, but haven't had a chance to do a super deep dive.
Overall question for LTO. For builds with tons of debug info. Say 2GB+ how many buckets we end up with that have cross CU references?

https://github.com/llvm/llvm-project/pull/197859