Macro safer_ffi::layout::ReprC

macro_rules! ReprC {
    (
    $(
        @[doc = $doc:expr]
    )?
    $(
        #[doc = $doc2:expr]
    )*
    #[repr(
        $C_or_transparent:ident $(,
            $($(@$if_js:tt)?
        js $(,)?
            )?
        )?
    )]
    $(
        #[$attr:meta]
    )*
    $pub:vis
    struct $StructName:ident $([$($generics:tt)*])?
    $(
        where { $($wc:tt)* }
    )?
    $({
        $($body:tt)*
    })?
    $((
        $($body2:tt)*
    );)?
) => { ... };
}

Transitioning helper macro: still uses the old ReprC! syntax, but just to forward to the new #[derive_ReprC2($(js)?)] one.