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

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trcrsired wrote:

> This could close #54868 that I had opened a while back to support cross compiling using clang with [xwin](https://github.com/Jake-Shadle/xwin/).

no. I do not want that complicated file structure. I just want normal GNU style's sysroot

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