Add string.h header file to directory listing implementations.

runtime/bin/directory_macos.cc

 // Copyright (c) 2012, 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 "bin/directory.h"
 
 #include <dirent.h>
 #include <errno.h>
+#include <string.h>
 #include <sys/param.h>
 #include <sys/stat.h>
 #include <unistd.h>
 
 #include "bin/file.h"
 #include "bin/platform.h"
 
 class PathBuffer {
  public:
   PathBuffer() : length(0) { }
@@ skipping 380 matching lines @@
     return DeleteRecursively(dir_name);
   }
 }
 
 
 bool Directory::Rename(const char* path, const char* new_path) {
   ExistsResult exists = Exists(path);
   if (exists != EXISTS) return false;
   return (TEMP_FAILURE_RETRY(rename(path, new_path)) == 0);
 }