Introduce a vastly simpler VIR_INT64_STR_BUFLEN constant
which is large enough for all cases where we currently
use INT_BUFSIZE_BOUND. This eliminates most use of the
gnulib intprops.h header.
Reviewed-by: NPavel Hrdina <phrdina@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>