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.

m4/mbsrtowcs.m4

@@ -0,0 +1,123 @@
+# mbsrtowcs.m4 serial 7
+dnl Copyright (C) 2008-2010 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_FUNC_MBSRTOWCS],
+[
+  AC_REQUIRE([gl_WCHAR_H_DEFAULTS])
+
+  AC_REQUIRE([AC_TYPE_MBSTATE_T])
+  gl_MBSTATE_T_BROKEN
+
+  AC_CHECK_FUNCS_ONCE([mbsrtowcs])
+  if test $ac_cv_func_mbsrtowcs = no; then
+    HAVE_MBSRTOWCS=0
+  else
+    if test $REPLACE_MBSTATE_T = 1; then
+      REPLACE_MBSRTOWCS=1
+    else
+      gl_MBSRTOWCS_WORKS
+      case "$gl_cv_func_mbsrtowcs_works" in
+        *yes) ;;
+        *) REPLACE_MBSRTOWCS=1 ;;
+      esac
+    fi
+  fi
+  if test $HAVE_MBSRTOWCS = 0 || test $REPLACE_MBSRTOWCS = 1; then
+    gl_REPLACE_WCHAR_H
+    AC_LIBOBJ([mbsrtowcs])
+    AC_LIBOBJ([mbsrtowcs-state])
+    gl_PREREQ_MBSRTOWCS
+  fi
+])
+
+dnl Test whether mbsrtowcs works.
+dnl Result is gl_cv_func_mbsrtowcs_works.
+
+AC_DEFUN([gl_MBSRTOWCS_WORKS],
+[
+  AC_REQUIRE([AC_PROG_CC])
+  AC_REQUIRE([gt_LOCALE_FR_UTF8])
+  AC_REQUIRE([gt_LOCALE_JA])
+  AC_REQUIRE([gt_LOCALE_ZH_CN])
+  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+  AC_CACHE_CHECK([whether mbsrtowcs works],
+    [gl_cv_func_mbsrtowcs_works],
+    [
+      dnl Initial guess, used when cross-compiling or when no suitable locale
+      dnl is present.
+changequote(,)dnl
+      case "$host_os" in
+                          # Guess no on HP-UX and Solaris.
+        hpux* | solaris*) gl_cv_func_mbsrtowcs_works="guessing no" ;;
+                          # Guess yes otherwise.
+        *)                gl_cv_func_mbsrtowcs_works="guessing yes" ;;
+      esac
+changequote([,])dnl
+      if test $LOCALE_FR_UTF8 != none || test $LOCALE_JA != none || test $LOCALE_ZH_CN != none; then
+        AC_RUN_IFELSE(
+          [AC_LANG_SOURCE([[
+#include <locale.h>
+#include <string.h>
+#include <wchar.h>
+int main ()
+{
+  /* Test whether the function works when started with a conversion state
+     in non-initial state.  This fails on HP-UX 11.11 and Solaris 10.  */
+  if (setlocale (LC_ALL, "$LOCALE_FR_UTF8") != NULL)
+    {
+      const char input[] = "B\303\274\303\237er";
+      mbstate_t state;
+
+      memset (&state, '\0', sizeof (mbstate_t));
+      if (mbrtowc (NULL, input + 1, 1, &state) == (size_t)(-2))
+        if (!mbsinit (&state))
+          {
+            const char *src = input + 2;
+            if (mbsrtowcs (NULL, &src, 10, &state) != 4)
+              return 1;
+          }
+    }
+  if (setlocale (LC_ALL, "$LOCALE_JA") != NULL)
+    {
+      const char input[] = "<\306\374\313\334\270\354>";
+      mbstate_t state;
+
+      memset (&state, '\0', sizeof (mbstate_t));
+      if (mbrtowc (NULL, input + 3, 1, &state) == (size_t)(-2))
+        if (!mbsinit (&state))
+          {
+            const char *src = input + 4;
+            if (mbsrtowcs (NULL, &src, 10, &state) != 3)
+              return 1;
+          }
+    }
+  if (setlocale (LC_ALL, "$LOCALE_ZH_CN") != NULL)
+    {
+      const char input[] = "B\250\271\201\060\211\070er";
+      mbstate_t state;
+
+      memset (&state, '\0', sizeof (mbstate_t));
+      if (mbrtowc (NULL, input + 1, 1, &state) == (size_t)(-2))
+        if (!mbsinit (&state))
+          {
+            const char *src = input + 2;
+            if (mbsrtowcs (NULL, &src, 10, &state) != 4)
+              return 1;
+          }
+    }
+  return 0;
+}]])],
+          [gl_cv_func_mbsrtowcs_works=yes],
+          [gl_cv_func_mbsrtowcs_works=no],
+          [:])
+      fi
+    ])
+])
+
+# Prerequisites of lib/mbsrtowcs.c.
+AC_DEFUN([gl_PREREQ_MBSRTOWCS], [
+  :
+])