[clang] [llvm] [StrTable] Switch diag group names to `llvm::StringTable` (PR #123302)

[David Blaikie via llvm-commits]

https://github.com/dwblaikie approved this pull request.

Generally looks fine to me - given the central nature of the data structure, wouldn't mind a second/more authoritative set of eyes if someone has time.

You mention the performance tradeoff of pascal strings v null terminated ones doesn't seem too important - I guess that's based on some judgement about where/how these are used/where the strlens end up happening that you've looked into? Could you summarize that in a bit more detail (like they only happen during diagnostic processing, or something?)

https://github.com/llvm/llvm-project/pull/123302