[clang] Switch builtin strings to use string tables (PR #118734)

[Chandler Carruth via cfe-commits]

chandlerc wrote:

(FYI, I'm about to drop offline -- Hans, if you think it makes sense to revert temporarily, please feel free to do so. I don't have a good sense of whether the fallout here is enough to warrant that.)

https://github.com/llvm/llvm-project/pull/118734