[llvm] [llvm-profgen] Support creating profiles of arbitrary events (PR #99026)

[via llvm-commits]

WenleiHe wrote:

> I will prepare another PR to address your review comments.

Thanks. I went over the patch and I think we'd have a cleaner and more compatible implementation if this is all handled as part of callstack sample rather than lbr sample. If we do that, it might actually be easier to unland this first and review/reland a reworked version.

https://github.com/llvm/llvm-project/pull/99026