[clang] Enable c++20 modules support for c++23preview in clang-cl (PR #173663)

[Chuanqi Xu via cfe-commits]

https://github.com/ChuanqiXu9 commented:

LGTM. But I'd like to ask other reviewers to take another look.

CC @MaskRay @sharadhr @zmodem 

https://github.com/llvm/llvm-project/pull/173663