[clang] [CIR][EH] Implement codegen for dynamic exception specification (PR #224375)

[Andy Kaylor via cfe-commits]

andykaylor wrote:

Rebasing this on top of trunk introduced nine more cases that hit the `"emitStartEHSpec noexcept terminate scope"`. I'm not sure why, but it looks like I might need to implement that piece in this PR.

https://github.com/llvm/llvm-project/pull/224375