Use gnulib-tool to create gnulib source files.

* Add gnulib files generated by gnulib-tool in build-aux, m4 and
    grub-core/gnulib directories
    * .bzignore: Add **/.deps and autogenerated gnulib files
    * configure.ac: Assign auxiliary directory to build-aux, add invocation
    of gnulib macros, add grub-core/gnulib/Makefile
    * Makefile.am: Add gnulib directory in SUBDIRS (removing unnecessary .),
    include m4 directory to aclocal.
    * Makefile.util.def: Remove direct compilation of gnulib source files
    and use the new grub-core/gnulib/libgnu.a.
    * build-aux/config.rpath: move config.rpath from top directory to
    build-aux
    * conf/Makefile.common: Remove the macro _GL_UNUSED already defined
    in gnulib headers
    * conf/Makefile.extra-dist: Add m4/gnulib-cache.m4
    * grub-core/Makefile.core.def: Remove unnecessary extra_dist
    * grub-core/lib/posix_wrap/localcharset.h (locale_charset): Update
    header.
    * grub-core/lib/posix_wrap/langinfo.h (nl_langinfo): Return static
    string.

grub-core/gnulib/realloc.c

@@ -0,0 +1,91 @@
+/* realloc() function that is glibc compatible.
+
+   Copyright (C) 1997, 2003-2004, 2006-2007, 2009-2010 Free Software
+   Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* written by Jim Meyering and Bruno Haible */
+
+#include <config.h>
+
+/* Only the AC_FUNC_REALLOC macro defines 'realloc' already in config.h.  */
+#ifdef realloc
+# define NEED_REALLOC_GNU 1
+/* Whereas the gnulib module 'realloc-gnu' defines HAVE_REALLOC_GNU.  */
+#elif GNULIB_REALLOC_GNU && !HAVE_REALLOC_GNU
+# define NEED_REALLOC_GNU 1
+#endif
+
+/* Infer the properties of the system's malloc function.
+   The gnulib module 'malloc-gnu' defines HAVE_MALLOC_GNU.  */
+#if GNULIB_MALLOC_GNU && HAVE_MALLOC_GNU
+# define SYSTEM_MALLOC_GLIBC_COMPATIBLE 1
+#endif
+
+/* Below we want to call the system's malloc and realloc.
+   Undefine the symbols here so that including <stdlib.h> provides a
+   declaration of malloc(), not of rpl_malloc(), and likewise for realloc.  */
+#undef malloc
+#undef realloc
+
+/* Specification.  */
+#include <stdlib.h>
+
+#include <errno.h>
+
+/* Below we want to call the system's malloc and realloc.
+   Undefine the symbols, if they were defined by gnulib's <stdlib.h>
+   replacement.  */
+#undef malloc
+#undef realloc
+
+/* Change the size of an allocated block of memory P to N bytes,
+   with error checking.  If N is zero, change it to 1.  If P is NULL,
+   use malloc.  */
+
+void *
+rpl_realloc (void *p, size_t n)
+{
+  void *result;
+
+#if NEED_REALLOC_GNU
+  if (n == 0)
+    {
+      n = 1;
+
+      /* In theory realloc might fail, so don't rely on it to free.  */
+      free (p);
+      p = NULL;
+    }
+#endif
+
+  if (p == NULL)
+    {
+#if GNULIB_REALLOC_GNU && !NEED_REALLOC_GNU && !SYSTEM_MALLOC_GLIBC_COMPATIBLE
+      if (n == 0)
+        n = 1;
+#endif
+      result = malloc (n);
+    }
+  else
+    result = realloc (p, n);
+
+#if !HAVE_REALLOC_POSIX
+  if (result == NULL)
+    errno = ENOMEM;
+#endif
+
+  return result;
+}