block-sha1: Use '(B&C)+(D&(B^C))' instead of '(B&C)|(D&(B|C))' in round 3

block-sha1: Use '(B&C)+(D&(B^C))' instead of '(B&C)|(D&(B|C))' in round 3

It's an equivalent expression, but the '+' gives us some freedom in
instruction selection (for example, we can use 'lea' rather than 'add'),
and associates with the other additions around it to give some minor
scheduling freedom.

Suggested-by: linux@horizon.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>