[clang] [Driver] Print C++ standard library info (PR #207798)

[Yaxun Liu via cfe-commits]

yxsamliu wrote:

@trcrsired Re: PR #96417 interaction

Thanks for pointing this out. I was not aware of PR #96417 when I made this change.

The two PRs use `AddClangCXXStdlibIncludeArgs` differently. PR #96417 uses it during normal `clang++ --sysroot=...` compilation to add the C++ header paths. My change uses it to report the standard MSVC include paths for `--print-cxx-stdlib-include-dirs`. Keeping only either implementation will break the other case.

I think PR #96417 should keep its current logic when `--sysroot` is present and use `AddMSVCStdlibIncludeArgs` for the print option when there is no custom sysroot. The existing MSVC tests in `print-cxx-stdlib.cpp` should also be kept. I will be happy to help review PR #96417 so it can accommodate the merged change and support both layouts.

https://github.com/llvm/llvm-project/pull/207798