[llvm] [FileCheck]: Fix diagnostic for trailing CHECK-NOT (PR #78412)

[Vinayak Dev via llvm-commits]

vinayakdsci wrote:

> I feel what we need is to change DagNotStrings to be a vector of FileCheckString instead of a vector of Pattern since it's FileCheckString that associate a Prefix, Loc and Pattern. All we need then is to create FileCheckString for CHECK-NOTs and CHECK-DAGs with an empty DagNotStrings for them.
> 
> Does that make sense?

That is one if the approaches I tried, but I was hesitant to push it. Should I go ahead?

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