Only run this new test on macOS

Author: DougGregor

test/ModuleInterface/SilencePreconcurrency.swiftinterface

@@ -4,4 +4,6 @@
 // RUN: %empty-directory(%t)
 // RUN: %target-swift-frontend -compile-module-from-interface -o %/t/SilencePreconcurrency.swiftmodule %s -verify
 
+// REQUIRES: OS=macosx
+
 @preconcurrency import Swift