Use #if TARGET_OS_IOS instead of #ifdef TARGET_OS_IOS.

runtime/bin/file_system_watcher_macos.cc

 // Copyright (c) 2013, 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"
 #if defined(TARGET_OS_MACOS)
 
 #include "bin/file_system_watcher.h"
 
-#if !defined(TARGET_OS_IOS)
+#if !TARGET_OS_IOS
 
 #include <errno.h>  // NOLINT
 #include <fcntl.h>  // NOLINT
 #include <unistd.h>  // NOLINT
 #include <CoreServices/CoreServices.h>  // NOLINT
 
 #include "bin/eventhandler.h"
 #include "bin/fdutils.h"
 #include "bin/file.h"
 #include "bin/socket.h"
@@ skipping 366 matching lines @@
     Dart_ListSetAt(event, 3, Dart_NewBoolean(true));
     Dart_ListSetAt(event, 4, Dart_NewInteger(path_id));
     Dart_ListSetAt(events, i, event);
   }
   return events;
 }
 
 }  // namespace bin
 }  // namespace dart
 
-#else  // !defined(TARGET_OS_IOS)
+#else  // !TARGET_OS_IOS
 
 namespace dart {
 namespace bin {
 
 // FSEvents are unavailable on iOS. Stub out related methods
 Dart_Handle FileSystemWatcher::ReadEvents(intptr_t id, intptr_t path_id) {
   return DartUtils::NewDartOSError();
 }
 
 intptr_t FileSystemWatcher::GetSocketId(intptr_t id, intptr_t path_id) {
@@ skipping 17 matching lines @@
 intptr_t FileSystemWatcher::WatchPath(intptr_t id,
                                       const char* path,
                                       int events,
                                       bool recursive) {
   return -1;
 }
 
 }  // namespace bin
 }  // namespace dart
 
-#endif  // !defined(TARGET_OS_IOS)
+#endif  // !TARGET_OS_IOS
 
 #endif  // defined(TARGET_OS_MACOS)