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

[via cfe-commits]

yronglin wrote:

I have run msan stage2 build, only 1 failure encountered, seems it's not related to this PR. Is there any way to tigger a buildbot on this PR?
```
27.56s: LLVM :: CodeGen/AMDGPU/shufflevector.v2i16.v8i16.ll
27.36s: Clang :: CodeGen/X86/sse42-builtins.c

Tests Times:
--------------------------------------------------------------------------
[    Range    ] :: [               Percentage               ] :: [    Count    ]
--------------------------------------------------------------------------
[80.0s,85.0s) :: [                                        ] :: [     1/113167]
[75.0s,80.0s) :: [                                        ] :: [     1/113167]
[70.0s,75.0s) :: [                                        ] :: [     0/113167]
[65.0s,70.0s) :: [                                        ] :: [     0/113167]
[60.0s,65.0s) :: [                                        ] :: [     0/113167]
[55.0s,60.0s) :: [                                        ] :: [     1/113167]
[50.0s,55.0s) :: [                                        ] :: [     0/113167]
[45.0s,50.0s) :: [                                        ] :: [     1/113167]
[40.0s,45.0s) :: [                                        ] :: [     3/113167]
[35.0s,40.0s) :: [                                        ] :: [     3/113167]
[30.0s,35.0s) :: [                                        ] :: [     6/113167]
[25.0s,30.0s) :: [                                        ] :: [    10/113167]
[20.0s,25.0s) :: [                                        ] :: [    24/113167]
[15.0s,20.0s) :: [                                        ] :: [    46/113167]
[10.0s,15.0s) :: [                                        ] :: [   171/113167]
[ 5.0s,10.0s) :: [                                        ] :: [   650/113167]
[ 0.0s, 5.0s) :: [*************************************** ] :: [112250/113167]
--------------------------------------------------------------------------
********************
Failed Tests (1):
  MLIR-Unit :: Target/LLVM/./MLIRTargetLLVMTests/MLIRTargetLLVMNVVM/SerializeNVVMToBinary


Testing Time: 1226.40s

Total Discovered Tests: 130823
  Skipped          :     23 (0.02%)
  Unsupported      :   2449 (1.87%)
  Passed           : 128128 (97.94%)
  Expectedly Failed:    222 (0.17%)
  Failed           :      1 (0.00%)
```

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