[NaCl SDK] Fix SDK waterfall: unistd.h does not exist on windows.

native_client_sdk/src/libraries/nacl_io/mount_mem.cc

 /* 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.
  */
 #include "nacl_io/mount_mem.h"
 
 #include <errno.h>
 #include <fcntl.h>
-#include <unistd.h>
 
 #include <string>
 
 #include "nacl_io/mount.h"
 #include "nacl_io/mount_node.h"
 #include "nacl_io/mount_node_dir.h"
 #include "nacl_io/mount_node_mem.h"
 #include "nacl_io/osstat.h"
+#include "nacl_io/osunistd.h"
 #include "nacl_io/path.h"
 #include "sdk_util/auto_lock.h"
 #include "sdk_util/ref_object.h"
 
 MountMem::MountMem() : root_(NULL), max_ino_(0) {}
 
 Error MountMem::Init(int dev, StringMap_t& args, PepperInterface* ppapi) {
   Error error = Mount::Init(dev, args, ppapi);
   if (error)
     return error;
@@ skipping 212 matching lines @@
     return ENOTDIR;
 
   if (file_only && child->IsaDir())
     return EISDIR;
 
   if (remove_dir && child->ChildCount() > 0)
     return ENOTEMPTY;
 
   return parent->RemoveChild(path.Basename());
 }