This reverts commit 557359f92512ca88b62a602ebda291f17a953002, reversing changes made to 1e6c09a803fd543a98bfbe1624d697a55300a786.
NaiveLayout
Still more complexity, but this allows computing exact `NaiveLayout`s for null-optimized enums, and thus allows calls like `transmute::<Option<&T>, &U>()` to work in generic contexts.