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

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trcrsired wrote:

https://github.com/Jake-Shadle/xwin/issues/138

https://github.com/rust-cross/cargo-xwin

Oh i rememebered wrong. it was cargo-xwin that uses it.

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