A task without an unwinder will abort the process on failure.
I'm using this in the runtime tests to guarantee that a call to
`assert!` actually triggers some kind of failure (an abort)
instead of silently doing nothing. This is essentially in lieu
of a working linked failure implementation.
Things like the GC heap and unwinding are desirable everywhere the language
might be used, not just in tasks. All Rust code should have access to
LocalServices.
