Fix Dartium build

runtime/bin/process_unsupported.cc

 // Copyright (c) 2016, 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.
 
 #if defined(DART_IO_DISABLED)
 
 #include "bin/process.h"
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
 #include "include/dart_api.h"
 
 namespace dart {
 namespace bin {
 
 int Process::global_exit_code_ = 0;
 Mutex* Process::global_exit_code_mutex_ = new Mutex();
 Process::ExitHook Process::exit_hook_ = NULL;
 
 void Process::TerminateExitCodeHandler() {}
 
+void Process::ClearAllSignalHandlers() {}
 
 void FUNCTION_NAME(Process_Start)(Dart_NativeArguments args) {
   Dart_ThrowException(
       DartUtils::NewInternalError("Process is not supported on this platform"));
 }
 
 
 void FUNCTION_NAME(Process_Wait)(Dart_NativeArguments args) {
   Dart_ThrowException(
       DartUtils::NewInternalError("Process is not supported on this platform"));
@@ skipping 56 matching lines @@
 
 void FUNCTION_NAME(StringToSystemEncoding)(Dart_NativeArguments args) {
   Dart_ThrowException(
       DartUtils::NewInternalError("Process is not supported on this platform"));
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // !defined(DART_IO_DISABLED)