This strategy adds another field to the SwitchBr instruction,
which is the result of the CheckSwitchProngs instruction. The
type of the result is void, and is unused, except that the SwitchBr
instruction will not perform analysis if the CheckSwitchProngs
instruction did not pass analysis. This allows the CheckSwitchProngs
instruction to do implicit casting for its type checking, while
preventing duplicate compile error messages.