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

[via cfe-commits]

trcrsired wrote:

Hello everyone,

I have completed all the necessary updates:

- Switched from -stdlib=stl to -stdlib=msstl.
- Added documentation detailing usage of --sysroot.
- Applied minor adjustments to suppress warnings triggered by setting msstl in CXXStdlibType, which affects multiple backends.
- 

Note: The -stdlib=msstl flag also applies to MinGW. It's possible that the mingw-w64 project could explore integration with Microsoft's STL.

Additionally, ntdll.dll is now consistently linked alongside kernel32.dll. All supported Windows versions are NT-based, and even legacy systems like Windows 95 include ntdll.dll.

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