swift234

Import CF types as managed pointers when they are:
  - the type of a const global variable
  - the type of a parameter, always
  - the return type of a function that has been audited
    or has an explicit retained/not-retained attribute
  - the return type of an ObjC method that has an explicit
    retain/not-retained/inner-pointer attribute

Additionally, choose the correct conventions for all
these cases during SIL type lowering.

All this importing logic is still only enabled under
-Xfrontend -import-cf-types.

Swift SVN r17543