[ORC] Deallocate FinalizedAllocs on error paths in notifyEmitted.

If notifyEmitted encounters a failure (either because some plugin returned one,
or because the ResourceTracker was defunct) then we need to deallocate the
FinalizedAlloc manually.

No testcase yet: This requires a concurrent setup -- we'll need to build some
infrastructure to coordinate links and deliberately injected failures in order
to reliably test this.