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

[Baranov Victor via cfe-commits]

vbvictor wrote:

P.S.
One of the comments in the original issue was right about annoyance with CI integration.
I started [tinkering with `clang-tidy` CI for LLVM](https://github.com/vbvictor/llvm-project/pull/2) and stumbled upon this. I'd need to also enhance `-quiet` mode in scripts because for now it gives such output:

```console
Running clang-tidy for 446 files out of 5099 in compilation database ...
[  1/446][3.6s] clang-tidy-21 -p=build/ -quiet /home/victor/llvm2/llvm-project/clang-tools-extra/clang-tidy/misc/ConfusableTable/BuildConfusableTable.cpp
33046 warnings generated.
```

The last string will be suppressed in this PR and the first and second lines should be suppressed inside `run-clang-tidy`



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