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

[Congcong Cai via cfe-commits]

HerrCai0907 wrote:

> Why can the tests not just accept reference files that do not contain any CHECK-* comments?

run-clang-tidy do assert for this, since FileCheck need to use this information to check the result. If nothing is provided, then  nothing can be detected.

> 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?

`not` will treat non-zero return code as success. It is totally different thing. 

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