block-sha1: split the different "hacks" to be individually selected This is to make it easier for them to be selected individually depending on the architecture instead of the other way around i.e. having each architecture select a list of hacks up front. That makes for clearer documentation as well. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>