[clang] [clang] Support --sysroot= for ${arch}-windows-msvc targets (PR #96417)

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trcrsired wrote:

![image](https://github.com/user-attachments/assets/23cb90b1-c47d-4804-af14-676f5a649e15)
See wasm. xxx-windows-gnu. aarch64-linux-android. x86_64-linux-gnu etc. They all have exactly the same file structures. I do not see why should xxx-windows-msvc should be different from x86_64-windows-gnu. /winsysroot and clang-cl thing just complicates everything. The thing that pisses me off is that clang does not enforce a standard rule for all targets but every target rewrites its rule that needs to stop tbh.

https://github.com/llvm/llvm-project/pull/96417