2ddbbd4735
Updates two points in the compiler that were easy to miss when adding new terminals: * HIRBuilder's `removeUnreachableFallthroughs()` nulls out unreachable fallthroughs, but this had a non-exhaustive `if` statement. It now uses a helper function which internally has an exhaustive switch. * LeaveSSA needs to schedule block fallthroughs, but had a non-exhaustive `if` statement. It also uses a helper function which internally has an exhaustive switch. cc @poteto since you ran into this (ie the compiler not alerting you to update these places) w your diffs.