Macro lazy_arc

macro_rules! lazy_arc {
    ($(#[$attr:meta])* $vis:vis static ref $N:ident : Arc<$T:ty> = $e:expr; $($rest:tt)*) => { ... };
    (@arc, $(#[$attr:meta])* $vis:vis static ref $N:ident : Arc<$T:ty> = $e:expr) => { ... };
    () => { ... };
}