Add regression test for https://bugs.swift.org/browse/SR-4211

Author: slavapestov

validation-test/Serialization/SR4211.swift

@@ -0,0 +1,13 @@
+// RUN: %target-build-swift -emit-module %s
+
+// REQUIRES: objc_interop
+import Foundation
+
+/// Set of notifications that can be sent by this manager
+extension Notification.Name {
+    /// Notifications that can be posted by the BLE code.
+    class BLE {
+        /// A notification posted when a new device has been discovered while scanning.
+        static var discoveredDevice = Notification.Name("my_unique_notification name")
+    }
+}