[clang-tools-extra] [clang-tidy] new check readability-mark-static (PR #90830)

[Congcong Cai via cfe-commits]

HerrCai0907 wrote:

> Add support for unity builds (.cpp files included from single .cpp file = isInMainFile is not sufficient)

For unity build, it looks like a project level decision. Then they can ignore this check. Maybe I can provide an option to treat some extension as main file also.

https://github.com/llvm/llvm-project/pull/90830