[clang] [clang] Fix crash in dynamic_cast final class optimization (PR #152076)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

> LLVM Buildbot has detected a new failure on builder `lldb-aarch64-ubuntu` running on `linaro-lldb-aarch64-ubuntu` while building `clang` at step 6 "test".
> 
> Full details are available at: https://lab.llvm.org/buildbot/#/builders/59/builds/22214
> 
> Here is the relevant piece of the build log for the reference

Sigh, let's see what configuration I broke

https://github.com/llvm/llvm-project/pull/152076