[clang] Support C++20 Modules in clang-repl (PR #79261)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

> Hi @ChuanqiXu9, the test you added is failing on the PS4 bot because for the PS4 target, it requires an external linker which is not present/available. Can the test be rewritten to not require linking?
> 
> https://lab.llvm.org/buildbot/#/builders/139/builds/57928
> 
> ```
> clang: error: unable to execute command: Executable "orbis-ld" doesn't exist!
> clang: error: linker command failed with exit code 1 (use -v to see invocation)
> ```

Oh, maybe I need to add more requires to the test.

https://github.com/llvm/llvm-project/pull/79261