[clang] [clang] [modules] Add err_main_in_named_module (PR #146247)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

FWIW, I fixed it in https://github.com/llvm/llvm-project/commit/5186d4aeeeca56a77404c2842e494524b7cdd4ba to avoid affecting more people longer.

https://github.com/llvm/llvm-project/pull/146247