Import Gnulib modules: link, fsync, readlink, rename, mkdir, rmdir, unistd.

* lib/fsync.c:
* lib/link.c:
* lib/mkdir.c:
* lib/strdup.c:
* m4/fsync.m4:
* m4/link.m4:
* m4/mkdir.m4:
* m4/strdup.m4: New files.

* lib/Makefile.am
* m4/gnulib-cache.m4
* m4/gnulib-comp.m4: Add modules.

lib/strdup.c

@@ -0,0 +1,54 @@
+/* Copyright (C) 1991, 1996-1998, 2002-2004, 2006-2007, 2009-2014 Free Software
+   Foundation, Inc.
+
+   This file is part of the GNU C Library.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License along
+   with this program; if not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef _LIBC
+# include <config.h>
+#endif
+
+/* Get specification.  */
+#include <string.h>
+
+#include <stdlib.h>
+
+#undef __strdup
+#ifdef _LIBC
+# undef strdup
+#endif
+
+#ifndef weak_alias
+# define __strdup strdup
+#endif
+
+/* Duplicate S, returning an identical malloc'd string.  */
+char *
+__strdup (const char *s)
+{
+  size_t len = strlen (s) + 1;
+  void *new = malloc (len);
+
+  if (new == NULL)
+    return NULL;
+
+  return (char *) memcpy (new, s, len);
+}
+#ifdef libc_hidden_def
+libc_hidden_def (__strdup)
+#endif
+#ifdef weak_alias
+weak_alias (__strdup, strdup)
+#endif