[clang] [lldb] [Clang] Improve Sema diagnostic performance for __builtin_counted_by_ref (PR #116719)

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Sirraide wrote:

> I image @AaronBallman is on vacation this week. @Sirraide would you be willing to LGTM this so that I can move it along?

I mean, this is stricly a performance issue, so I’m not sure why we’d want to merge it this urgently...

https://github.com/llvm/llvm-project/pull/116719