grub2: does not build with prerelease autoconf

Originally reported to Fedora as
https://bugzilla.redhat.com/show_bug.cgi?id=2183156 :

> Autoconf 2.72 (or 2.73) seems to be under preparation upstream, I
> therefore started to build dependent components against the
> pre-release [1] to verify that they can be built once it lands in
> Fedora.
>
> Your component fails to build with the new version of autoconf, due to
> the following error:
>
> configure:9900: error: possibly undefined macro:
> _AC_SYS_LARGEFILE_TEST_INCLUDES
>       If this token and others are legitimate, please use m4_pattern_allow.
>       See the Autoconf documentation.
> autoreconf: error: /usr/bin/autoconf failed with exit status: 1
>
> Unfortunately, this can't be fixed with an autoreconf, an update of the
> files provided by gnulib are necessary.
> These files are usually added during the bootstrap of the source code,
> which is done to generate the release tarball.

They further clarified that we need a gnulib update to at least
7c7c8a519f ("largefile: sync from Autoconf master").

This is not a trivial update (not that gnulib updates ever are).  gnulib
has split the bootstrap script into many files.  Also, it breaks some of
our symbol definitions, and I didn't look further into it.

Be well,
--Robbie

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