[clang] [llvm] [ThinLTO] Support dead RTTI data elimination under -fno-split-lto-unit (PR #126336)

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luxufan wrote:

> Taking a further look shows these preserved RTTIs come from vtables whose superclass has its type-id accessed.

Thank you for helping evaluate this patch. I am curious about what this type ID is used for—is it for dynamic_cast, exception handling, or the typeid operator?

https://github.com/llvm/llvm-project/pull/126336