Mirror 4363197 from Dev-Framework

Perform a placeholder resolve pass immediately after the CDO has been serialized
#rb Mike.Beach
#jira UE-62928

#ROBOMERGE-SOURCE: CL 4433763 in //UE4/Release-4.21/...
#ROBOMERGE-BOT: RELEASE (Release-4.21 -> Release-Staging-4.21)

[CL 4433765 by dan oconnor in Staging-4.21 branch]

Engine/Source/Runtime/CoreUObject/Public/UObject/LinkerLoad.h

@@ -80,6 +80,7 @@ class FLinkerLoad
 	friend class UObject;
 	friend class UPackageMap;
 	friend struct FAsyncPackage;
+	friend struct FResolvingExportTracker;
 protected:
 	/** Linker loading status. */
 	enum ELinkerStatus
@@ -1081,6 +1082,9 @@ private:
 	 */
 	void ResolveDeferredExports(UClass* LoadClass);
 
+	/** Called when a class is loaded and its now safe to load deferred instances */
+	void ResolvePlaceholder(ULinkerPlaceholderExportObject* Placeholder);
+
 	/** Helper function to recursively resolve placeholders that were waiting for their outer */
 	void ResolvedDeferredSubobjects(ULinkerPlaceholderExportObject* OwningPlaceholder);