builtin-`derive` errors when encountering macros in type position

[lcnr]

macro_rules! mk_u32 {
    () => { u32 }
}

#[derive(Clone)]
struct Foo {
    value: mk_u32!(), // ok
}

#[derive(Clone)]
struct Bar<T> {
    param: T,
    value: mk_u32!(), // error
}