[clang] [CIR] Add NYI cases to builtin switch statement and move existing cases into functions (PR #168699)

[Andy Kaylor via cfe-commits]

andykaylor wrote:

> Sure, that would be very useful. I need two people to request commit access, right?

Yes. When you request access, the tool will automatically tag people who have approved your PRs. I don't expect that it will be a problem getting a second supporter.

https://github.com/llvm/llvm-project/pull/168699