cksum: resolve msvc unsafe issue
cksum: resolve msvc unsafe issue

Fixes #886

kevgeniy/coreutils,uutils/coreutils,Heather/coreutils,uutils/coreutils,uutils/coreutils,wimh/coreutils,jbcrail/coreutils,kevgeniy/coreutils,jbcrail/coreutils,kwantam/coreutils,keunwoo/coreutils,Heather/coreutils,ebfe/coreutils,kwantam/coreutils,ebfe/coreutils,Arcterus/coreutils,Arcterus/coreutils,tempbottle/coreutils,wimh/coreutils,tempbottle/coreutils,keunwoo/coreutils