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

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llvmbot wrote:

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Failed to cherry-pick: 9d315bc

https://github.com/llvm/llvm-project/actions/runs/10294654014

Please manually backport the fix and push it to your github fork.  Once this is done, please create a [pull request](https://github.com/llvm/llvm-project/compare)

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