This commit makes minor changes to the cranelift backend so that it can
build given changes in cg_ssa for Split DWARF.
Signed-off-by: David Wood <david@davidtw.co>
with an eye on merging `TargetOptions` into `Target`.
`TargetOptions` as a separate structure is mostly an implementation detail of `Target` construction, all its fields logically belong to `Target` and available from `Target` through `Deref` impls.