In file included from util/grub-mkimage.c:54:0:
./grub-core/gnulib/argp.h:627:49: error: '__sbistype' is static but
used in inline function '_option_is_short' which is not static
[-Werror] cc1: all warnings being treated as errors gmake[2]: ***
[util/grub_mkimage-grub-mkimage.o] Error 1

Update m4/extern-inline.m4 to current upstream gnulib version that
contains fix for this (commit b9bfe78424b871f5b92e5ee9e7d21ef951a6801d).
Reported-By: Beeblebrox <zaphod@berentweb.com>

* grub-core/gnulib/stdio.in.h (gets): Warn on use only if
HAVE_RAW_DECL_GETS.
* m4/stdio_h.m4 (gl_STDIO_H): Check for gets.

* configure.ac: Create po/Makefile.in rather than po/Makefile.
* grub-core/gnulib/Makefile.am: Import gettext module.
* m4/gnulib-cache.m4: Likewise.
* m4/gnulib-comp.m4: Likewise.
* m4/gettext.m4: New file, from gnulib.
* m4/glibc2.m4: Likewise.
* m4/iconv.m4: Likewise.
* m4/intdiv0.m4: Likewise.
* m4/intl.m4: Likewise.
* m4/intldir.m4: Likewise.
* m4/intlmacosx.m4: Likewise.
* m4/intmax.m4: Likewise.
* m4/inttypes-pri.m4: Likewise.
* m4/lcmessage.m4: Likewise.
* m4/lib-ld.m4: Likewise.
* m4/lib-link.m4: Likewise.
* m4/lib-prefix.m4: Likewise.
* m4/lock.m4: Likewise.
* m4/nls.m4: Likewise.
* m4/po.m4: Likewise.
* m4/printf-posix.m4: Likewise.
* m4/progtest.m4: Likewise.
* m4/threadlib.m4: Likewise.
* m4/uintmax_t.m4: Likewise.
* m4/visibility.m4: Likewise.
* po/Makefile.am: Remove.
* po/Makefile.in.in: New file, from gettext.
($(DOMAIN).pot-update): Support POTFILES-shell.
* po/Makevars: New file.
* po/POTFILES-shell: Rename to ...
* po/POTFILES-shell.in: ... this.  Update.
* po/POTFILES: Rename to ...
* po/POTFILES.in: ... this.  Update.
* po/Rules-quot: New file, from gettext.
* po/boldquot.sed: Likewise.
* po/en@boldquot.header: Likewise.
* po/en@quot.header: Likewise.
* po/insert-header.sin: Likewise.
* po/quot.sed: Likewise.
* po/remove-potcdate.sin: Likewise.

    * 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.