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

[Andrzej Warzyński via cfe-commits]

https://github.com/banach-space commented:

I've only had one point re LLVM and @matthias-springer has already raised that.

I've left a question re test formatting. I'm mostly just curious - I am adding some tests myself and want to find ways to reduce CHECK lines. This looks like a similar case.

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