[NFC] Document the solution to pr61006 and a test for it

Address https://github.com/llvm/llvm-project/issues/61006.

The actual reason for the issue is about the usage of clang-scan-deps
instead of its functionalities since clang-scan-deps has
already considered the problem before for clang modules.

So this patch tries to document the corresponding solution
and add a test case for it to address the issue.