/// will be properly aligned. Note that the result layout will
/// satisfy the alignment properties of both `self` and `next`.
///
+ /// The resulting layout will be the same as that of a C struct containing
+ /// two fields with the layouts of `self` and `next`, in that order.
+ ///
/// Returns `Some((k, offset))`, where `k` is layout of the concatenated
/// record and `offset` is the relative location, in bytes, of the
/// start of the `next` embedded within the concatenated record