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

[via cfe-commits]

trcrsired wrote:

> The most obvious, first-party way to set up an MSVC ABI + MSVC STL cross-compile environment on Unix-like environments would be to use the above installer on Windows itself or maybe WINE and install it to a case-insensitive FS, mount that filesystem on the Unix-like host, and then write `clang --sysroot=...`. If you are running `clang` on your Android phone, this would entail copy-pasting the Windows SDK and MSVC STL into an SD card, loading it up, and then writing `clang --sysroot=/sdcard/VC/...` or something similar.

What world are you living in? There is no sdcard any more. In fact Apple is trying to create portless iphone with no ports at all. Users have been gradually losing their rights to their own property. You will own nothing and you will be happy, World economic forum 2030

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