[test] Confess that Unmanaged’s hacky Equatable conformance is retroactive

Author: lorentey

Tests/AtomicsTests/Basics/BasicTestSupport.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift Atomics open source project
 //
-// Copyright (c) 2020 - 2023 Apple Inc. and the Swift project authors
+// Copyright (c) 2020 - 2025 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See https://swift.org/LICENSE.txt for license information
@@ -12,11 +12,19 @@
 
 import Atomics
 
+#if compiler(>=6.0)
+extension Unmanaged: @retroactive Equatable { // FIXME: This is terrible
+  public static func ==(left: Self, right: Self) -> Bool {
+    left.toOpaque() == right.toOpaque()
+  }
+}
+#else
 extension Unmanaged: Equatable { // FIXME: This is terrible
   public static func ==(left: Self, right: Self) -> Bool {
     left.toOpaque() == right.toOpaque()
   }
 }
+#endif
 
 struct Foo: Equatable, CustomStringConvertible {
   var value: Int