@objc enums have special requirements on the raw type, which were
enforced as part of checking the raw type of the enum. Rework the
checking here so that the additional constraints are part of resolving
whether the enum is exposed to Objective-C. This keeps raw-type
computation more independent and “lower-level” than @objc computation.
Once reworked, eliminate the “CIntegerTypes” cache from TypeChecker:
it probably doesn't matter, and the caching should be performed by the
request-evaluator rather than the type checker.
For @objc enums, raw values determine the representation values, so we have
to compute them eagerly in order for switch statements to work. Similarly,
if the enum is broken, we have to /fail/ eagerly so that we don't fall down
later on in IRGen.
rdar://problem/19775284
Swift SVN r25282
