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/sysexits.in.h

@@ -0,0 +1,71 @@
+/* exit() exit codes for some BSD system programs.
+   Copyright (C) 2003, 2006-2010 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 Simon Josefsson based on sysexits(3) man page */
+
+#ifndef _GL_SYSEXITS_H
+
+#if __GNUC__ >= 3
+@PRAGMA_SYSTEM_HEADER@
+#endif
+
+#if @HAVE_SYSEXITS_H@
+
+/* IRIX 6.5 has an <unistd.h> that defines a macro EX_OK with a nonzero
+   value.  Override it.  See
+   <http://lists.gnu.org/archive/html/bug-gnulib/2007-03/msg00361.html>  */
+# ifdef __sgi
+#  include <unistd.h>
+#  undef EX_OK
+# endif
+
+/* The include_next requires a split double-inclusion guard.  */
+# @INCLUDE_NEXT@ @NEXT_SYSEXITS_H@
+
+/* HP-UX 11 <sysexits.h> ends at EX_NOPERM.  */
+# ifndef EX_CONFIG
+#  define EX_CONFIG 78
+# endif
+
+#endif
+
+#ifndef _GL_SYSEXITS_H
+#define _GL_SYSEXITS_H
+
+#if !@HAVE_SYSEXITS_H@
+
+# define EX_OK 0 /* same value as EXIT_SUCCESS */
+
+# define EX_USAGE 64
+# define EX_DATAERR 65
+# define EX_NOINPUT 66
+# define EX_NOUSER 67
+# define EX_NOHOST 68
+# define EX_UNAVAILABLE 69
+# define EX_SOFTWARE 70
+# define EX_OSERR 71
+# define EX_OSFILE 72
+# define EX_CANTCREAT 73
+# define EX_IOERR 74
+# define EX_TEMPFAIL 75
+# define EX_PROTOCOL 76
+# define EX_NOPERM 77
+# define EX_CONFIG 78
+
+#endif
+
+#endif /* _GL_SYSEXITS_H */
+#endif /* _GL_SYSEXITS_H */