Previously, switches over extremely large integers (e.g. i832) were
emitted when emitting switches with many spare bits. Such switches
result in unfortunate downstream codegen.
Here, for large enums (currently, more than two words) the preexisting
EnumPayload::emitCompare function is used to compare each of the enum
cases in turn with the payload's value. The result is a series of
cond_br where the conditional is made by anding together word-size
chunks of the payload value with word-size chunks of each enum case's
tag, subject to masking.
rdar://83158525
