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

[Erich Keane via cfe-commits]

erichkeane wrote:

> MLIR side looks good, but can you also add test cases to `mlir/test/Target/LLVMIR/Import/function-attributes.ll`, `mlir/test/Target/LLVMIR/llvmir.mlir` and `mlir/test/Dialect/LLVMIR/func.mlir`? (Do the same as for `willreturn`.)

Thanks for the quick review!  I wasn't aware of those tests!  My first pass through writing those tests copying off of willreturn seems to have not been successful, so I'll spend some time on it.

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