Macro make_ffi_fn_defs

macro_rules! make_ffi_fn_defs {
    {
        $(
            $(#[$fn_attr:meta])*
            fn $fn_name:ident($($fn_arg_name:ident: $fn_arg_type:ty),*) $(-> $fn_ret_ty:ty)?;
        )*
    } => { ... };
}