[clang] [C++][Modules] A module directive may only appear as the first preprocessing tokens in a file (PR #144233)

[Adrian Vogelsgesang via cfe-commits]

vogelsgesang wrote:

Should this commit also mark the papers as implemented on https://clang.llvm.org/cxx_status.html?

https://github.com/llvm/llvm-project/pull/144233