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

[Piotr Zegar via cfe-commits]

PiotrZSL wrote:

> Isn't this already covered by `-Wmissing-prototypes`?

No, because -Wmissing-prototypes will not provide warning, when both declaration and definition is in .cpp

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