Really remove io support when dart:io is unsupported.

runtime/bin/io_impl_sources.gypi

 # 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.
 
 # This file contains some C++ sources for the dart:io library.  The other
 # implementation files are in builtin_impl_sources.gypi.
 {
   'sources': [
     'eventhandler.cc',
     'eventhandler.h',
     'eventhandler_android.cc',
     'eventhandler_android.h',
     'eventhandler_linux.cc',
     'eventhandler_linux.h',
     'eventhandler_macos.cc',
     'eventhandler_macos.h',
+    'eventhandler_unsupported.cc',
     'eventhandler_win.cc',
     'eventhandler_win.h',
     'file_system_watcher.cc',
     'file_system_watcher.h',
     'file_system_watcher_android.cc',
     'file_system_watcher_linux.cc',
     'file_system_watcher_macos.cc',
+    'file_system_watcher_unsupported.cc',
     'file_system_watcher_win.cc',
     'filter.cc',
     'filter.h',
     'filter_unsupported.cc',
     'io_service.cc',
     'io_service.h',
     'io_service_no_ssl.cc',
     'io_service_no_ssl.h',
     'io_service_unsupported.cc',
     'platform.cc',
     'platform.h',
     'platform_android.cc',
     'platform_linux.cc',
     'platform_macos.cc',
+    'platform_unsupported.cc',
     'platform_win.cc',
     'process.cc',
     'process.h',
     'process_android.cc',
     'process_linux.cc',
     'process_macos.cc',
+    'process_unsupported.cc',
     'process_win.cc',
     '../../third_party/root_certificates/root_certificates.cc',
     'root_certificates_unsupported.cc',
     'secure_socket.h',
     'secure_socket_boringssl.cc',
     'secure_socket_boringssl.h',
     'secure_socket_macos.cc',
     'secure_socket_macos.h',
     'secure_socket_unsupported.cc',
     'socket.cc',
     'socket.h',
     'socket_android.cc',
     'socket_android.h',
     'socket_linux.cc',
     'socket_linux.h',
     'socket_macos.cc',
     'socket_macos.h',
+    'socket_unsupported.cc',
     'socket_win.cc',
     'socket_win.h',
     'stdio.cc',
     'stdio.h',
     'stdio_android.cc',
     'stdio_linux.cc',
     'stdio_macos.cc',
+    'stdio_unsupported.cc',
     'stdio_win.cc',
   ],
-  'conditions': [
-    ['dart_io_support==1', {
-      'sources!' : [
-        'filter_unsupported.cc',
-        'io_service_unsupported.cc',
-      ],
-    },{  # else dart_io_support == 0
-      'sources!' : [
-        'filter.cc',
-        'filter.h',
-        'io_service.cc',
-        'io_service.h',
-        'io_service_no_ssl.cc',
-        'io_service_no_ssl.h',
-        '../../third_party/root_certificates/root_certificates.cc',
-        'root_certificates_unsupported.cc',
-        'secure_socket.h',
-        'secure_socket_boringssl.cc',
-        'secure_socket_boringssl.h',
-        'secure_socket_macos.cc',
-        'secure_socket_macos.h',
-      ],
-    }],
-  ],
 }