Merge pull request swiftlang#63074 from xedin/rdar-104354485

[AST] Adjust `getBridgedToObjC` to produce only valid witness types

Author: xedin

lib/AST/ASTContext.cpp

@@ -5464,7 +5464,10 @@ Type ASTContext::getBridgedToObjC(const DeclContext *dc, Type type,
       *bridgedValueType = type;
 
     // Find the Objective-C class type we bridge to.
-    return conformance.getTypeWitnessByName(type, Id_ObjectiveCType);
+    Type witnessTy = conformance.getTypeWitnessByName(type, Id_ObjectiveCType);
+    // If Objective-C import is broken, witness type would be a dependent member
+    // with `<<error type>>` base.
+    return (witnessTy && !witnessTy->hasError()) ? witnessTy : Type();
   }
 
   // Do we conform to Error?