[clang] [llvm] [Clang] Make exact dynamic_cast optimization AS aware (PR #213927)

[Nikolas Klauser via llvm-commits]

https://github.com/philnik777 commented:

I'm _very_ surprised that this isn't actually at all related to the `type_info` magic, but just a general pattern that can occur anywhere.

https://github.com/llvm/llvm-project/pull/213927