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

[Nikita Popov via cfe-commits]

nikic wrote:

This causes a large compile-time regression: https://llvm-compile-time-tracker.com/compare.php?from=1b5d6ec6855369d109fcb740ecd3812231b7a279&to=ea321392ebc487c1000e43576f44af99edf28a5f&stat=instructions:u

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