I am writing firmware rn for a device of which I expect multiple to be connected at the same time so to make it clear which is which, I wanna give it its own PID and product name on the USB...
I'm trying to do this with the cfg macro rn
https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-macro
```
        let mut usb_dev = if cfg!(FO) {
                UsbDeviceBuilder::new(&usb_bus, UsbVidPid(0x16c0, 0x27db))
                .manufacturer("FLC Meow")
                .product("MCDU First Officer")
                .serial_number("01189998819991197253")
                .build();
        } else if cfg!(third) {
                UsbDeviceBuilder::new(&usb_bus, UsbVidPid(0x16c0, 0x27dc))
                .manufacturer("FLC Meow")
                .product("MCDU 3rd Occupant")
                .serial_number("01189998819991197253")
                .build();
        } else {
                UsbDeviceBuilder::new(&usb_bus, UsbVidPid(0x16c0, 0x27da))
                .manufacturer("FLC Meow")
                .product("MCDU Captain")
                .serial_number("01189998819991197253")
                .build();
        };
```
but later on it throws this error:
```
error[E0599]: no method named `poll` found for unit type `()` in the current scope
   --> src/main.rs:198:14
    |
198 |         if usb_dev.poll(&mut [&mut consumer]) {
    |                    ^^^^ method not found in `()`
```