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/strncasecmp.c

@@ -0,0 +1,63 @@
+/* strncasecmp.c -- case insensitive string comparator
+   Copyright (C) 1998-1999, 2005-2007, 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, 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, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <string.h>
+
+#include <ctype.h>
+#include <limits.h>
+
+#define TOLOWER(Ch) (isupper (Ch) ? tolower (Ch) : (Ch))
+
+/* Compare no more than N bytes of strings S1 and S2, ignoring case,
+   returning less than, equal to or greater than zero if S1 is
+   lexicographically less than, equal to or greater than S2.
+   Note: This function cannot work correctly in multibyte locales.  */
+
+int
+strncasecmp (const char *s1, const char *s2, size_t n)
+{
+  register const unsigned char *p1 = (const unsigned char *) s1;
+  register const unsigned char *p2 = (const unsigned char *) s2;
+  unsigned char c1, c2;
+
+  if (p1 == p2 || n == 0)
+    return 0;
+
+  do
+    {
+      c1 = TOLOWER (*p1);
+      c2 = TOLOWER (*p2);
+
+      if (--n == 0 || c1 == '\0')
+        break;
+
+      ++p1;
+      ++p2;
+    }
+  while (c1 == c2);
+
+  if (UCHAR_MAX <= INT_MAX)
+    return c1 - c2;
+  else
+    /* On machines where 'char' and 'int' are types of the same size, the
+       difference of two 'unsigned char' values - including the sign bit -
+       doesn't fit in an 'int'.  */
+    return (c1 > c2 ? 1 : c1 < c2 ? -1 : 0);
+}