[clang-tools-extra] [clang-tidy] Improve "-quiet" option by suppressing "xxx warnings generated" (PR #154012)

[Baranov Victor via cfe-commits]

vbvictor wrote:

> LGTM, thanks for fixing!
> 
> It might be worth double-checking the comment I wrote about this carets option (which I guess is equivalent to passing the command line flag):
> 
> [#47042 (comment)](https://github.com/llvm/llvm-project/issues/47042#issuecomment-1305630120)
> 
> In particular the fact that part of the diagnostic is removed. But perhaps it's only for compiler warnings and it's not a problem for clang-tidy.

Thanks for the issue link and concerns!

Yes, it doesn't affect `clang-tidy` because there are 2 separate `DiagnosticOptions` we can set in `clang-tidy`.
The first `ClangTidyDiagnosticConsumer` that has one set of `DiagnosticOptions` is left unchanged:
https://github.com/llvm/llvm-project/blob/a10773c8646d482e8747ca37d5a51523505ffbb7/clang-tools-extra/clang-tidy/ClangTidy.cpp#L574-L578
And second one for `CompilerInvocation` that handles `warnings generated` but passes all actual diagnostics to consumer (`clang-tidy` in our case).

I've added tests with carets (hopefully correctly) so this feature will be tracked in the future.

https://github.com/llvm/llvm-project/pull/154012