Bitwidth zero for discriminants

[jberthold]

Since we cannot reliably determine the discriminant bit width from layout, we:

• set bitwidth to 0 for values obtained from the RValue Discriminant
• allow comparisons using these discriminant values on either side of comparison operations
• allow these discriminants to be used in switchInt terminators

[dkcumming]

Looks good, we might want an issue that is backlog saying to see if we can get to the bottom of what the type will really be (sounds like a big time sink of research and confusion)

[jberthold]

Looks good, we might want an issue that is backlog saying to see if we can get to the bottom of what the type will really be (sounds like a big time sink of research and confusion)

#793 created