Macro extern_fns 

macro_rules! extern_fns {
    (
        $(#[doc = $doc:literal])*
        #[link_name = $link_name:literal]
        $vis:vis fn $ident:ident ($($arg:ident : $arg_ty:ty),* $(,)?);
        $($rest:tt)*
    ) => { ... };
    (
        $(#[doc = $doc:literal])*
        #[link_name = $link_name:literal]
        $vis:vis fn $ident:ident ($($arg:ident : $arg_ty:ty),* $(,)?) -> $ret_ty:ty;
        $($rest:tt)*
    ) => { ... };
    () => { ... };
}