[C++20] [Modules] clang-cl.exe doesn't work with C++20 modules with the HelloWorld example

[ChuanqiXu9]

Reported from https://discourse.llvm.org/t/clang-cl-exe-support-for-c-modules/72257/14

Simply, we can't use /clang:"..." form to compile C++20 modules with the HelloWorld example. But it works to use GNU style options with clang.exe in Windows. So it should be a driver issue.

[llvmbot]

@llvm/issue-subscribers-clang-modules

[llvmbot]

@llvm/issue-subscribers-clang-driver

[huangqinjin]

@ChuanqiXu9 Could you please have a look at #89772 ?

After that, clang-cl does work with C++20 named modules and header units using /clang: (tested in huangqinjin/cxxmodules@d03268b).

The only issue I observed is the warning

clang-cl: warning: argument unused during compilation: '/std:c++20' [-Wunused-command-line-argument]

[llvmbot]

@llvm/issue-subscribers-c-20

Author: Chuanqi Xu (ChuanqiXu9)

Reported from https://discourse.llvm.org/t/clang-cl-exe-support-for-c-modules/72257/14

Simply, we can't use /clang:"..." form to compile C++20 modules with the HelloWorld example. But it works to use GNU style options with clang.exe in Windows. So it should be a driver issue.