[VS Addin] Fix parallel building.

visual_studio/NativeClientVSAddIn/NaCl.Build.CPPTasks/NaClCompile.cs

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 using System;
 using System.Collections.Generic;
 using System.Text;
 using System.Collections;
 using System.IO;
 using System.Reflection;
 using System.Resources;
@@ skipping 355 matching lines @@
                     srcGroups.Add(commandLine, new List<ITaskItem> {sourceItem});
                 }
             }
 
             string pythonScript = Path.GetDirectoryName(Path.GetDirectoryName(PropertiesFile));
             pythonScript = Path.Combine(pythonScript, "compiler_wrapper.py");
 
             foreach (KeyValuePair<string, List<ITaskItem>> entry in srcGroups)
             {
                 string commandLine = entry.Key;
-                string cmd = "\"" + pathToTool + "\" " + commandLine + "--";
+                string cmd = "\"" + pathToTool + "\" " + commandLine + " --";
                 List<ITaskItem> sources = entry.Value;
 
                 foreach (ITaskItem sourceItem in sources)
                 {
+                    cmd += " ";
                     cmd += GCCUtilities.ConvertPathWindowsToPosix(sourceItem.ToString());
                 }
 
                 try
                 {
                     // compile this group of sources
                     returnCode = base.ExecuteTool("python", cmd, "\"" + pythonScript + "\"");
                 }
                 catch (Exception e)
                 {
@@ skipping 148 matching lines @@
         protected override string ToolName
         {
             get
             {
                 return NaCLCompilerPath;
             }
         }
 
     }
 }