[llvm] [FileCheck]: Fix diagnostics for NOT prefixes (PR #78412)

[Thomas Preud'homme via llvm-commits]

RoboTux wrote:

> @RoboTux I apologise, but I am a tad bit confused what you mean when you say that I would want to modify printMatch and printNotMatch to handle CheckNot.
> 
> Do you mean I need to modify their definitions? I could simply pass in the correct prefix through reportMatchResult being called in CheckDag() and CheckNot(); Wouldn't that make it immaterial what Prefix is exactly held at CheckStr.Check(), if the current prefix is a DAG or NOT string?
> 
> All other suggestions you gave I have already incorporated, and been able to get all tests to pass satisfactorily.
> 
> Thanks a lot!

No my bad, it was me who missed something. It looks good now, thanks!

https://github.com/llvm/llvm-project/pull/78412