[llvm] [llvm-profgen][NFC] Detect pre-aggregated format (PR #191593)

[via llvm-commits]

HighW4y2H3ll wrote:

Why do we need to restrict buildID annotation only for LBRStack samples? It looks like the current implementation is compatible with the pre-aggregated input and if there's no aggregated count the default will be 1:
https://github.com/llvm/llvm-project/blob/b9998b1f104aa0fd0a443ac91932debef595893a/llvm/tools/llvm-profgen/PerfReader.cpp#L1048-L1054

https://github.com/llvm/llvm-project/pull/191593