[clang] [llvm] [PAC][clang] Fix ptrauth module flags behavior (PR #204226)

[Anatoly Trosinenko via cfe-commits]

https://github.com/atrosinenko approved this pull request.

LGTM with minor comments (I assume they can be addressed by rather straightforward changes to only three test files) but please address the comment of @jchlanda and update the PR description accordingly (now the change is described as restricted to only two module flags).

https://github.com/llvm/llvm-project/pull/204226