Merge pull request #2950 from spevans/pr_sr_12981_54

[5.4] SR-12981: Foundation.StreamDelegate has required methods on Linux but not Darwin

Author: spevans

Sources/Foundation/Stream.swift

@@ -323,14 +323,15 @@ extension Stream {
 }
 #endif
 
-extension StreamDelegate {
-    func stream(_ aStream: Stream, handle eventCode: Stream.Event) { }
-}
 
 public protocol StreamDelegate : class {
     func stream(_ aStream: Stream, handle eventCode: Stream.Event)
 }
 
+extension StreamDelegate {
+    public func stream(_ aStream: Stream, handle eventCode: Stream.Event) { }
+}
+
 // MARK: -
 extension Stream.PropertyKey {
     public static let socketSecurityLevelKey = Stream.PropertyKey(rawValue: "kCFStreamPropertySocketSecurityLevel")