This test is known to fail on a debug stdlib

aschwaighofer · aschwaighofer · commit 50068d880af6 · 2016-08-03T14:51:30.000-07:00
rdar://27226313 (cherry picked from commit b5a8805)
diff --git a/test/1_stdlib/Dispatch.swift b/test/1_stdlib/Dispatch.swift
@@ -3,6 +3,9 @@
 
 // REQUIRES: objc_interop
 
+// rdar://27226313
+// REQUIRES: optimized_stdlib
+
 import Dispatch
 import Foundation
 import StdlibUnittest
