macro_rules! cfg_asm {
    (@inner, [$($x:tt)*], [$($opts:tt)*], ) => { ... };
    (@inner, [$($x:tt)*], [$($opts:tt)*], #[cfg($meta:meta)] $asm:literal, $($rest:tt)*) => { ... };
    (@inner, [$($x:tt)*], [$($opts:tt)*], $asm:literal, $($rest:tt)*) => { ... };
    ({$($asms:tt)*}, $($opts:tt)*) => { ... };
}