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

[Vinayak Dev via llvm-commits]

vinayakdsci wrote:

@RoboTux I have rebased and pushed the code. Had to push twice because clang-format also auto-formatted CMakeLists.txt.

Please do take a look at the code once you find time. It fixes the issues you presented yesterday. I made all attempts to change the original code as little as possible. Also, it was difficult to declare DagNotMatches as a vector of FileCheckString because then DagNotStrings would require a linear time update to extract the patterns(it is declared under FileCheckString too, so it wouldn't be possible to declare DagNotStrings as a vector of FileCheckString!).

Thanks!

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