Fix calls to pthread_join

runtime/vm/os_thread_macos.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"  // NOLINT
 #if defined(TARGET_OS_MACOS)
 
 #include "vm/os_thread.h"
 
 #include <sys/errno.h>  // NOLINT
@@ skipping 143 matching lines @@
   return ThreadIdFromIntPtr(pthread_mach_thread_np(pthread_self()));
 }
 
 
 ThreadJoinId OSThread::GetCurrentThreadJoinId() {
   return pthread_self();
 }
 
 
 void OSThread::Join(ThreadJoinId id) {
-  ASSERT(pthread_join(id, NULL) == 0);
+  int result = pthread_join(id, NULL);
+  ASSERT(result == 0);
 }
 
 
 intptr_t OSThread::ThreadIdToIntPtr(ThreadId id) {
   ASSERT(sizeof(id) == sizeof(intptr_t));
   return reinterpret_cast<intptr_t>(id);
 }
 
 
 ThreadId OSThread::ThreadIdFromIntPtr(intptr_t id) {
@@ skipping 194 matching lines @@
 
 void Monitor::NotifyAll() {
   // TODO(iposva): Do we need to track lock owners?
   int result = pthread_cond_broadcast(data_.cond());
   VALIDATE_PTHREAD_RESULT(result);
 }
 
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)