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

[Chandler Carruth via cfe-commits]

https://github.com/chandlerc commented:

> Fails to build with GCC:

Doh, I had hoped GCC would support this. Anyways, fixed back to just suppress the diagnostic with Clang. Did some builds with GCC and everything seems fine, and it doesn't seem like we're GCC warning clean these days anyways.

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