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

[Alexander Richardson via llvm-commits]

arichardson 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`?

Technically I guess the whole file is IR but I can't think of a better name that isn't super long (`--check-comments-in-function`). So this sounds good to me.

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