swift234

Handle CF <-> Objective-C toll-free-bridged conversions in the type checker.

Introduce an attribute that describes when a given CF type is
toll-free-bridged to an Objective-C class, and which class that
is. Use that information in the type checker to provide the CF <->
Objective-C toll-free-bridged conversions directly, rather than using
the user-defined conversion machinery.

Swift SVN r21376