Fix Mac build.

runtime/bin/file_macos.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 <errno.h>
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <unistd.h>
 #include <libgen.h>
 
+#include "bin/builtin.h"
 #include "bin/file.h"
 
 class FileHandle {
  public:
   explicit FileHandle(int fd) : fd_(fd) { }
   ~FileHandle() { }
   int fd() const { return fd_; }
   void set_fd(int fd) { fd_ = fd; }
 
  private:
@@ skipping 98 matching lines @@
 
 
 const char* File::PathSeparator() {
   return "/";
 }
 
 
 const char* File::StringEscapedPathSeparator() {
   return "/";
 }