unexpected behavior inside struct, for feature-gated arguments

[thor314]

Attempting the following:

pub(crate) struct Args {
	cfg_if! {
		if #[cfg(feature = "my_feat")] {
			some_feature_gated_arg: u8,
			some_other_feature_gated_arg: u8,
		} else {}
	}
	// ...
}

causes compile time errors. This would have been helpful to note in the Readme/docs.