[clang] [ItaniumCXXABI] Mark RTTI type name as global unnamed_addr (PR #111343)

[Richard Smith via cfe-commits]

zygoloid wrote:

Specifically: we do perform address comparisons between these strings, so the address is significant. And we can have identical string content but different types:

- for types whose name involves anything with internal linkage
- for types with hidden visibility
- when loading a DSO using `RTLD_LOCAL`

so in a few cases allowing merging could be bad. Most of that only applies during dynamic linking. Do we have a guarantee that `unnamed_addr` is dropped before dynamic linking?

https://github.com/llvm/llvm-project/pull/111343