uutils coreutils: cp/install/mv/ln --suffix alone does not enable backup mode (silent data loss vs GNU)

determinebackupmode in src/uucore/src/lib/features/backupcontrol.rs only checks --backup/-b and returns BackupMode::None when only --suffix is given. GNU enables backup mode when --suffix is used alone defaulting to existing/numbered, or $VERSIONCONTROL. Affects cp, install, mv, ln which share th...