Don't compile io_service if io is not supported.

runtime/bin/io_service_unsupported.cc

Index: runtime/bin/io_service_unsupported.cc
diff --git a/runtime/bin/vmservice.h b/runtime/bin/io_service_unsupported.cc
similarity index 57%
copy from runtime/bin/vmservice.h
copy to runtime/bin/io_service_unsupported.cc
index 4dcf93f704aaf7e82fc4d54ab5dbd81d2c7ee64e..9e51ca19792fc940814207089371f2ae86e26d23 100644
--- a/runtime/bin/vmservice.h
+++ b/runtime/bin/io_service_unsupported.cc
@@ -2,16 +2,20 @@
 // 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.
 
-#ifndef BIN_VMSERVICE_H_
-#define BIN_VMSERVICE_H_
+#include "bin/builtin.h"
+#include "bin/dartutils.h"
 
 #include "include/dart_api.h"
 
+
 namespace dart {
 namespace bin {
 
+void FUNCTION_NAME(IOService_NewServicePort)(Dart_NativeArguments args) {
+  Dart_ThrowException(DartUtils::NewDartArgumentError(
+      "IOService is unsupported on this platform"));
+}
 
 }  // namespace bin
 }  // namespace dart
 
-#endif  // BIN_VMSERVICE_H_