[llvm] [BOLT][merge-fdata] Fix basic sample profile aggregation without LBR info (PR #118481)

[Paschalis Mpeis via llvm-commits]

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

Thanks @tdusnoki!

Regarding my requested changes, it think it is now in a good shape.
However, you need to address / reach consensus on @aaupov comment [here](https://github.com/llvm/llvm-project/pull/118481#discussion_r1871858490) before merging.

Optionally, you may embed the contents of the `.fdata` files to the `.test` files and use `split-file` like [here](https://github.com/llvm/llvm-project/pull/112328/files#diff-258c8369ada028a94418d4b18a53f597e84b8bba58d17336bd935941d9606c13).




https://github.com/llvm/llvm-project/pull/118481