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

[Paschalis Mpeis via llvm-commits]

paschalis-mpeis wrote:

Thanks for the extra tests @tdusnoki! I believe now @aaupov concerns should be addressed?

Another ask from my end is to drop the `bolt/test/Inputs/*.fdata` inputs as you now don't use them in the patch.

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