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

[Bill Wendling via cfe-commits]

bwendling wrote:

I image @AaronBallman is on vacation this week. @Sirraide would you be willing to LGTM this so that I can move it along? It's certainly better than what we have and I can address any concerns Aaron has afterwards.

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