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

[Hubert Tong via cfe-commits]

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

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

I think the `cxx_status.html` change should be kept as partial in this PR then.
@Bigcheese, your thoughts?

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