[llvm] Add initial support for SPE brstack format (PR #129231)

[Amir Ayupov via llvm-commits]

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

LGTM, thank you for contributing this. 
Do you have plans to include an end-to-end (binary) test, with perf data with SPE samples?

https://github.com/llvm/llvm-project/pull/129231