[clang-tools-extra] [clang-tidy] support expect no diagnosis test (PR #91293)

[Danny Mösch via cfe-commits]

SimplyDanny wrote:

Why can the tests not just accept reference files that do not contain any `CHECK-*` comments? Then, no separate argument would be needed. In fact, I still sometimes struggle to find the correct options, command line and `CHECK-*` syntax. More options further complicate the setup.

Also, isn't there the `// RUN: not %check_clang_tidy` (note the `not`) command to claim a test file doesn't trigger the specified checks?

https://github.com/llvm/llvm-project/pull/91293