[clang] [mlir] [CIR] Implement 'noreturn' attribute for functions/calls. (PR #177978)

[Andy Kaylor via cfe-commits]

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

Looks good to me. There are a couple of open questions about how to represent the attribute and how to name the test check prefixes, but I'd be fine with deferring both of those issues.

https://github.com/llvm/llvm-project/pull/177978