ea321392eb
This PR is 2nd part of [P1857R3](https://github.com/llvm/llvm-project/pull/107168) implementation, and mainly implement the restriction `A module directive may only appear as the first preprocessing tokens in a file (excluding the global module fragment.)`: [cpp.pre](https://eel.is/c++draft/cpp.pre): ``` module-file: pp-global-module-fragment[opt] pp-module group[opt] pp-private-module-fragment[opt] ``` We also refine tests use `split-file` instead of conditional macro. Signed-off-by: yronglin <yronglin777@gmail.com>