Macro check_cfg_feature

macro_rules! check_cfg_feature {
    ($feature:tt, $feature_lit:tt) => { ... };
    ($feature:tt, $feature_lit:tt : $($target_feature_lit:tt),*) => { ... };
    ($feature:tt, $feature_lit:tt, without cfg check: $feature_cfg_check:literal) => { ... };
}

🔬This is a nightly-only experimental API. (stdarch_internal)