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

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@@ -986,6 +989,14 @@ def warn_module_conflict : Warning<
   InGroup<ModuleConflict>;
 
 // C++20 modules
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yronglin wrote:

Yes, this restriction was not implemented yet. We can implement this in a separate patch.

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