The `immortal` flag means that the resulting object is immortal, i.e. it is
never deallocated and therefore doesn't need to be retained or released. In
OSSA the result of an `immortal` `raw_pointer_to_ref` has `none` ownership,
whereas the result of a non-`immortal` `raw_pointer_to_ref` is `owned` - the
instruction "creates" a new reference which must be consumed exactly once.
Accordingly, lowering out of OSSA inserts a `strong_retain` after a non-immortal
`raw_pointer_to_ref`.
Erik Eckstein
64693b59da