pub fn matches(&self, feature: &str) -> Option<bool> {
        match self {
            TargetFeatures::Unknown => None,
            TargetFeatures::Features(features) => Some(features.contains(feature)),
            TargetFeatures::All => Some(true),
        }
    }
Returns `Some(true)` if this feature is a match, `Some(false)` if it isn't, and `None` if
the set of target features is unknown.
target-spec/src/platform.rs