pub fn all_features(&self) -> [(BuildPlatform, &FeatureSet<'g>); 2] {
        [
            (BuildPlatform::Target, self.target_features()),
            (BuildPlatform::Host, self.host_features()),
        ]
    }
Returns the feature sets across the target and host build platforms.
guppy/src/graph/cargo/cargo_api.rs