[clang] [C++20][Modules] Implement P1857R3 Modules Dependency Discovery (PR #107168)

[Nikita Popov via cfe-commits]

nikic wrote:

It looks like this change has significant compile time impact (+0.5% at `O0`): https://llvm-compile-time-tracker.com/compare.php?from=469e5245987b3250a9ca675275d59c7c5d6bbb00&to=d2e62d902438bb5860f2376e818d797bf20daa7d&stat=instructions:u

Is that expected?

https://github.com/llvm/llvm-project/pull/107168