[llvm] [BOLT] Fix incorrect CU-indicies in gdb-index (PR #151927)

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itrofimow wrote:

Hi! Thanks
Could you @ayermolo please merge this PR for me? - I don't have write access.

Also, while you are at it, would you be able to give this tiny PR https://github.com/llvm/llvm-project/pull/151923 a look? - It's related fix about BOLT sometimes emitting `[0; 0)` ranges in address map

https://github.com/llvm/llvm-project/pull/151927