Close https://github.com/llvm/llvm-project/issues/62843. Previously when we compile .pcm files into .o files, the `-fmodule-file=<module-name>=<module-path>` option is ignored. This is conflicted with our consensus in https://github.com/llvm/llvm-project/issues/62707.
A step to address https://github.com/llvm/llvm-project/issues/62707. It is not user friendly enough to drop the implicitly generated path directly. Let's emit the warning first and drop it in the next version.