[clang] [clang][driver][clang-cl] Fix unused argument warning for `/std:c++20` for precompiled module inputs to `clang-cl` (PR #99300)

[Chuanqi Xu via cfe-commits]

https://github.com/ChuanqiXu9 commented:

Please add a test for this too. We can use any file ends with `.pcm` to mimic  module file in the Driver's test and we can use `CHECK-NOT:` to filter the warning.

https://github.com/llvm/llvm-project/pull/99300