[llvm] [BOLT][DWARF][NFC] Add parallelization for processing of DWO debug information (PR #100282)

[Amir Ayupov via llvm-commits]

https://github.com/aaupov approved this pull request.

LG overall, but tests make me uneasy: that we're opting in all of them and setting thread-count to a rather high value of 72 (more than CUs per test).

I would suggest reducing that to 4 so it's less suspicious.

Also, processing in parallel is not NFC to me, even if the output stays exactly the same (use significantly more resources). So I'd suggest dropping [NFC] from the title. 

https://github.com/llvm/llvm-project/pull/100282