[clang] [clang][Diagnostics] Highlight code snippets (PR #66514)

[via cfe-commits]

bgra8 wrote:

@AaronBallman 

> Do you see this crash with community clang and no downstream changes?

Yes I can reproduce it with a vanila `clang` built  from a git checkout at this version, but the problem is extremely sensitive to  the input headers, their content and defines (`-Dbla`) in the compilation command.

> But if we get any evidence that other downstreams or users are hitting this or the issue is happening for Google's test case with a vanilla Clang, then I agree that a revert is appropriate until we have a solution.

This was already reported by another user in https://github.com/llvm/llvm-project/issues/80127. 

@tbaederr 

> That is, unless https://github.com/llvm/llvm-project/commit/6d1d2c67e7597dc417c097d5027558b0159ed2e2 actually fixed the problem already, which would be good to check.

I already mentioned this does not fix the crash.

https://github.com/llvm/llvm-project/pull/66514