Correct the sign of exit codes for the process library.

runtime/bin/process_win.cc

 // Copyright (c) 2011, 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 <process.h>
 
 #include "bin/builtin.h"
 #include "bin/globals.h"
 #include "bin/process.h"
 #include "bin/eventhandler.h"
@@ skipping 186 matching lines @@
     snprintf(os_error_message, os_error_message_len, "OS Error %d", error_code);
   }
   os_error_message[os_error_message_len - 1] = '\0';
   return error_code;
 }
 
 
 static unsigned int __stdcall TerminationWaitThread(void* args) {
   ProcessInfo* process = reinterpret_cast<ProcessInfo*>(args);
   WaitForSingleObject(process->process_handle(), INFINITE);
-  DWORD exit_code;
-  BOOL ok = GetExitCodeProcess(process->process_handle(), &exit_code);
+  int exit_code;
+  BOOL ok = GetExitCodeProcess(process->process_handle(),
+                               reinterpret_cast<DWORD*>(&exit_code));
   if (!ok) {
     fprintf(stderr, "GetExitCodeProcess failed %d\n", GetLastError());
   }
-  intptr_t message[2] = { process->pid(), static_cast<intptr_t>(exit_code) };
+  int negative = 0;
+  if (exit_code == 255) {
+    exit_code = 1;
+    negative = 1;
+  }
+  if (exit_code < 0) {
+    exit_code = abs(exit_code);
+    negative = 1;
+  }
+  int message[3] = { process->pid(), exit_code, negative };
   DWORD written;
   ok = WriteFile(
       process->exit_pipe(), message, sizeof(message), &written, NULL);
-  if (!ok || written != 8) {
+  if (!ok || written != sizeof(message)) {
     fprintf(stderr, "FileWrite failed %d\n", GetLastError());
   }
   return 0;
 }
 
 
 int Process::Start(const char* path,
                    char* arguments[],
                    intptr_t arguments_length,
                    intptr_t* in,
@@ skipping 172 matching lines @@
       return false;
     }
   }
   return true;
 }
 
 
 void Process::Exit(intptr_t id) {
   RemoveProcess(id);
 }