Add missing include

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@272638 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/thread/thread.mutex/thread.lock/thread.lock.guard/variadic_mutex.pass.cpp

@@ -20,6 +20,8 @@
 #include <mutex>
 #include <cassert>
 
+#include "test_macros.h"
+
 struct TestMutex {
     bool locked = false;
     TestMutex() = default;