`--target=` when it thinks it's not needed.
In your nailing-cargo config, you can write something like
-`arch.RPI='arm-unknown-linux-gnueabihf'`. Then `nailing-cargo -ARPI`
+`arch.RPI='arm-unknown-linux-gnueabihf'`. Then `nailing-cargo -TRPI`
will DTRT. In fact, you do not even need to specify that particular
arch alias, since it is built-in to nailing-cargo.