[llvm] [Bolt] Add a new hidden option to perf2bolt for testing purpose (PR #163785)

[Paschalis Mpeis via llvm-commits]

paschalis-mpeis wrote:

> Additionally, we have opts::ReadPerfEvents with a similar purpose and similarly used in testing, can we unify the two options?

@aaupov that's the plan, to eventually replace my half-baked `ReadPerfEvents` flag :)

https://github.com/llvm/llvm-project/pull/163785