[clang] Reland "[Utils] add update-verify-tests.py" (#108630)" (PR #108658)

[Erich Keane via cfe-commits]

erichkeane wrote:

> > 
> 
> +1, it's why I stopped recommending this approach in my reviews.

While I agree for the most part, there are quite a few diagnostics that are absurdly verbose (particularly ones with "did you mean to FLOOP it?").  I think partial matches are good/fine, but they need enough of the diag to not be ambiguous.

https://github.com/llvm/llvm-project/pull/108658