[llvm] [UTC] CHECK-EMPTY instead of skipping blank lines (PR #165718)

[Alexander Richardson via llvm-commits]

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

I think this could potentially cause a lot of test churn when regenerating, so probably worth making it a new version. But I'll defer that decision to @nikic 

https://github.com/llvm/llvm-project/pull/165718