unable to delete files beginning with `-`

[ninedotnine]

rm (and various other Unix tools) accept -- as a terminator for arguments,
allowing everything which appears after to be understood as a filename:

» touch -- -Z --xxx
» tree 
.
├── --xxx
└── -Z
0 directories, 2 files
» trash -- -Z
» trash -- --xxx
» tree
.
├── --xxx
└── -Z
0 directories, 2 files
» rm -- --xxx      
» rm -- -Z
» tree
.
0 directories, 0 files