Log error for SPC

Author: sbomer

src/coreclr/tools/aot/ILCompiler.Build.Tasks/ComputeManagedAssembliesToCompileToNative.cs

@@ -160,10 +160,18 @@ public override bool Execute()
                 // Currently that's System.Private.* SDK assemblies and a bunch of framework assemblies.
                 if (nativeAotFrameworkAssembliesToUse.TryGetValue(assemblyFileName, out ITaskItem frameworkItem))
                 {
+                    Console.WriteLine("warning: Found {0} in {1}", assemblyFileName, frameworkItem.ItemSpec);
                     if (GetFileVersion(itemSpec).CompareTo(GetFileVersion(frameworkItem.ItemSpec)) > 0)
                     {
-                        // Allow OOB references with higher version to take precedence over the framework assemblies.
-                        list.Add(taskItem);
+                        if (assemblyFileName == "System.Private.CoreLib.dll")
+                        {
+                            Log.LogError($"Overriding System.Private.CoreLib.dll with a newer version is not supported. Attempted to use {itemSpec} instead of {frameworkItem.ItemSpec}.");
+                        }
+                        else
+                        {
+                            // Allow OOB references with higher version to take precedence over the framework assemblies.
+                            list.Add(taskItem);
+                        }
                     }
 
                     assembliesToSkipPublish.Add(taskItem);