maint: update to latest gnulib
    
    Usual update to latest gnulib status.  In particular this update
    fixes at least one issue that can be seen in libvirt, by silencing
    a valgrind detection of uninitialized memory:
    https://bugzilla.redhat.com/show_bug.cgi?id=1174147
    
    * .gnulib: Update to latest.
    * bootstrap: Resync to gnulib.
    
    Signed-off-by: Eric Blake <eblake@redhat.com>