[clang] Reapply "[C++20][Modules] Implement P1857R3 Modules Dependency Discovery" (PR #173130)

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yronglin wrote:

> @yronglin Did you run msan stage 2 builds locally?

Yes, I can reproduce locally. I try to build a debug & msan build to  investigating the root cause.


https://github.com/llvm/llvm-project/pull/173130