Merge branch 'main' into rebranch

Conflicts:
      lib/Basic/Platform.cpp

```
diff --git a/lib/Basic/Platform.cpp b/lib/Basic/Platform.cpp
index 240edfa144a..1797c87635f 100644
--- a/lib/Basic/Platform.cpp
+++ b/lib/Basic/Platform.cpp
@@ -200,10 +200,7 @@ StringRef swift::getPlatformNameForTriple(const llvm::Triple &triple) {
   case llvm::Triple::CUDA:
   case llvm::Triple::DragonFly:
   case llvm::Triple::DriverKit:
-<<<<<<< HEAD
   case llvm::Triple::ELFIAMCU:
-=======
->>>>>>> main
   case llvm::Triple::Emscripten:
   case llvm::Triple::Fuchsia:
   case llvm::Triple::HermitCore:
```

lib/Serialization/Serialization.cpp

@@ -1321,21 +1321,25 @@ void Serializer::writeInputBlock() {
     time_t importedHeaderModTime = 0;
     std::string contents;
     auto importedHeaderPath = Options.ImportedHeader;
+    std::string pchIncludeTree;
     // We do not want to serialize the explicitly-specified .pch path if one was
     // provided. Instead we write out the path to the original header source so
     // that clients can consume it.
     if (Options.ExplicitModuleBuild &&
         llvm::sys::path::extension(importedHeaderPath)
-            .ends_with(file_types::getExtension(file_types::TY_PCH)))
-      importedHeaderPath = clangImporter->getClangInstance()
-                               .getASTReader()
-                               ->getModuleManager()
-                               .lookupByFileName(importedHeaderPath)
-                               ->OriginalSourceFileName;
+            .ends_with(file_types::getExtension(file_types::TY_PCH))) {
+      auto *pch = clangImporter->getClangInstance()
+                      .getASTReader()
+                      ->getModuleManager()
+                      .lookupByFileName(importedHeaderPath);
+      pchIncludeTree = pch->IncludeTreeID;
+      importedHeaderPath = pch->OriginalSourceFileName;
+    }
 
     if (!importedHeaderPath.empty()) {
       contents = clangImporter->getBridgingHeaderContents(
-          importedHeaderPath, importedHeaderSize, importedHeaderModTime);
+          importedHeaderPath, importedHeaderSize, importedHeaderModTime,
+          pchIncludeTree);
     }
     assert(publicImportSet.count(bridgingHeaderImport));
     ImportedHeader.emit(ScratchRecord,