[llvm] [UTC] Support to test annotated IR (PR #165419)

[Kunqiu Chen via llvm-commits]

Camsyn wrote:

> We also have a --check-attributes option to check another subset of comments. Could you add a test showing whether the new --check-comments flag also checks the function attributes comment?

It does not.
`--check-comments` only checks IR comments, orthogonal to `--check-attributes`, which checks the function comments. 

Maybe we should rename this option to `--check-ir-comments`?

https://github.com/llvm/llvm-project/pull/165419