Handle recursive field drop and user-defined destructors about miri HOT 3 CLOSED

We already have ElaborateDrops in place, but this feature would likely be a lot easier to implement if rustc generated actual Mir for drop glue.

from miri.

@oli-obk Is enough of this done that we can close this? (due to #74)

from miri.

Nope, we still have some things not working (like Option<&T>, which is a Layout::RawNullablePointer. (in fact the tests for the impl for that just finished successfully)

I'm running the rustc run-pass tests now to see if any other cases pop up.

Also I don't think the following works:

struct Foo;
impl Drop for Foo { .. }

enum Bar {
    A(Box<i32>),
    B(Foo),
}

from miri.