base64: fix build (assuming rust-lang/rust#19594 is merged)
base64: fix build (assuming rust-lang/rust#19594 is merged)

polapl/coreutils,beni55/coreutils,retep998/coreutils,dbrgn/coreutils,kwantam/coreutils,Shir0kamii/coreutils,dbrgn/coreutils,sshling/coreutils,Gianbaoluo/coreutils,ebfe/coreutils,jbcrail/coreutils,bundai223/coreutils,mauricio/coreutils,polapl/coreutils,steveklabnik/coreutils,hexsel/coreutils,uutils/coreutils,retep998/coreutils,Shtong/coreutils,dennis/coreutils,steveklabnik/coreutils,samfoo/coreutils,filmor/coreutils,bundai223/coreutils,kball/coreutils,efuquen/coreutils,silvio/rust-coreutils,Heather/coreutils,samfoo/coreutils,keunwoo/coreutils,hexsel/coreutils,dbrgn/coreutils,tempbottle/coreutils,mauricio/coreutils,jbcrail/coreutils,silvio/rust-coreutils,uutils/coreutils,wimh/coreutils,kwantam/coreutils,Shir0kamii/coreutils,ebfe/coreutils,Arcterus/coreutils,efuquen/coreutils,kball/coreutils,Arcterus/coreutils,filmor/coreutils,tempbottle/coreutils,kevgeniy/coreutils,wimh/coreutils,Gianbaoluo/coreutils,Heather/coreutils,sshling/coreutils,uutils/coreutils,beni55/coreutils,kevgeniy/coreutils,keunwoo/coreutils,Shtong/coreutils,dennis/coreutils