Bad ambigous error typechecking

we're also running into this with this code example - I suspect the fix would be the same and there is something wrong when it comes to references/pointers and mutability:

#![feature(intrinsics)]

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

pub struct VaListImpl<'f>;

mod sealed_trait {
    pub trait VaArgSafe {}
}

impl<T> sealed_trait::VaArgSafe for *mut T {}
impl<T> sealed_trait::VaArgSafe for *const T {}

impl<'f> VaListImpl<'f> {
    /// Advance to the next arg.
    #[inline]
    pub unsafe fn arg<T: sealed_trait::VaArgSafe>(&mut self) {
        va_arg2(self);
    }
}

fn va_arg2<T: sealed_trait::VaArgSafe>(ap: &mut VaListImpl<'_>) {}

Originally posted by @CohenArthur in https://github.com/Rust-GCC/gccrs/issues/3032#issuecomment-2127439140