[llvm] [BOLT] Adding a unittest that covers Arm SPE PBT aggregation (PR #160095)

[Paschalis Mpeis via llvm-commits]

https://github.com/paschalis-mpeis approved this pull request.

Thanks Adam, looks good!

Left a comment on something we could consider in the future.
Please wait 1-2 days before merging in case there are any further comments.

(@mate-stodulka, anything more to add?)

https://github.com/llvm/llvm-project/pull/160095