Impl block after macro expansion triggers macro expansion recursion limit

I tried this code:

// ---- gccrs additions

#[lang = "sized"]
trait Sized {}

// ---- gccrs additions

#[lang = "clone"]
pub trait Clone: Sized {
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use = "cloning is often expensive and is not expected to have side effects"]
    fn clone(&self) -> Self;

    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    fn clone_from(&mut self, source: &Self) {
        *self = source.clone()
    }
}

mod impls {
    use super::Clone;

    macro_rules! impl_clone {
        ($($t:ty)*) => {
            $(
                #[stable(feature = "rust1", since = "1.0.0")]
                impl Clone for $t {
                    #[inline]
                    fn clone(&self) -> Self {
                        *self
                    }
                }
            )*
        }
    }

    impl_clone! { usize }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> Clone for *const T {
        #[inline]
        fn clone(&self) -> Self {
            *self
        }
    }
}

if the last impl block is commented out, or put before the macro call, like so:

// ---- gccrs additions

#[lang = "sized"]
trait Sized {}

// ---- gccrs additions

#[lang = "clone"]
pub trait Clone: Sized {
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use = "cloning is often expensive and is not expected to have side effects"]
    fn clone(&self) -> Self;

    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    fn clone_from(&mut self, source: &Self) {
        *self = source.clone()
    }
}

mod impls {
    use super::Clone;

    macro_rules! impl_clone {
        ($($t:ty)*) => {
            $(
                #[stable(feature = "rust1", since = "1.0.0")]
                impl Clone for $t {
                    #[inline]
                    fn clone(&self) -> Self {
                        *self
                    }
                }
            )*
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> Clone for *const T {
        #[inline]
        fn clone(&self) -> Self {
            *self
        }
    }

    impl_clone! { usize }
}

...then the code works. :/

Start by running the Rust reproducer and compare macro expansion when the impl block appears after versus before the macro call. Trace the macro expansion path involved in the recursion-limit failure; done means both arrangements compile without triggering unintended recursion.