Add a compatibily test for swift 3

Author: Brian King

test/Compatibility/override.swift

@@ -0,0 +1,11 @@
+// RUN: %target-typecheck-verify-swift -parse-as-library -swift-version 3
+
+class A { 
+  @objc func objcVirtualFunction() { } // expected-note{{overridden declaration is here}}
+}
+
+class B : A { }
+
+extension B { 
+  override func objcVirtualFunction() { } // expected-warning{{cannot override a non-dynamic class declaration from an extension}}
+}

test/decl/inherit/override.swift

@@ -1,4 +1,4 @@
-// RUN: %target-typecheck-verify-swift -parse-as-library
+// RUN: %target-typecheck-verify-swift -parse-as-library -swift-version 4
 
 @objc class ObjCClassA {}
 @objc class ObjCClassB : ObjCClassA {}