swift234

[Importer] Update CF_ENUM detection for changes in Foundation.

...and bump our "Foundation epoch" guard to 3 to match.

Long-term we should switch to an attribute for "yes, this is really a set
of enumerated constants" (and "this is a set of related bitmask options"),
but this unblocks things for now, and doesn't cause any issue if we end
up doing something else.

rdar://problem/20418505

Swift SVN r26944