[clang] [Tooling] Fix misleading progress report when files have multiple compile commands (PR #169640)

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zeyi2 wrote:

Hi, Aaron.

Could you please review this patch? It fixes a misleading progress report issue in Tooling (e.g. `[22/18]`) when files have multiple compile commands.

I have addressed previous feedback from vbvictor and zwuis, could you do some furthur reviews?

Thanks for your time. 

https://github.com/llvm/llvm-project/pull/169640