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/alloca.in.h

@@ -0,0 +1,56 @@
+/* Memory allocation on the stack.
+
+   Copyright (C) 1995, 1999, 2001-2004, 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, 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.  */
+
+/* Avoid using the symbol _ALLOCA_H here, as Bison assumes _ALLOCA_H
+   means there is a real alloca function.  */
+#ifndef _GL_ALLOCA_H
+#define _GL_ALLOCA_H
+
+/* alloca (N) returns a pointer to N bytes of memory
+   allocated on the stack, which will last until the function returns.
+   Use of alloca should be avoided:
+     - inside arguments of function calls - undefined behaviour,
+     - in inline functions - the allocation may actually last until the
+       calling function returns,
+     - for huge N (say, N >= 65536) - you never know how large (or small)
+       the stack is, and when the stack cannot fulfill the memory allocation
+       request, the program just crashes.
+ */
+
+#ifndef alloca
+# ifdef __GNUC__
+#  define alloca __builtin_alloca
+# elif defined _AIX
+#  define alloca __alloca
+# elif defined _MSC_VER
+#  include <malloc.h>
+#  define alloca _alloca
+# elif defined __DECC && defined __VMS
+#  define alloca __ALLOCA
+# else
+#  include <stddef.h>
+#  ifdef  __cplusplus
+extern "C"
+#  endif
+void *alloca (size_t);
+# endif
+#endif
+
+#endif /* _GL_ALLOCA_H */