This change adds basic handling for normal cleanups. This is a very
minimal implemention. In particular, it uses a naive substitute for the
rich cleanup and EH stack handling that is present in classic codegen
and the CIR incubator. This is intended as a temporary implementation to
allow incremental progress. It is not expected to scale well enough to
be used in a production environment. It will be replaced with the full
EHScopeStack handling when such an implementation is needed.
