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

[via cfe-commits]

trcrsired wrote:

Do we have any microsoft developers in this LLVM project? I am willing to negoiate with them to transfer thw windows-msvc-sysroot ownership to them to let them maintain the project.

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