swift234

[ClangImporter] Hack: import selected constants from Security as CFStrings.

This is a step towards making the framework easier to use in Swift; in the
actual headers, these are typed as "CFTypeRef" or "const CFTypeRef", which
is not considered Hashable (and thus cannot be put in a dictionary).
Unfortunately, CFStringRef is also not hashable, so we're not there yet,
but at least this allows a freer conversion to NSString.

Part of <rdar://problem/17162475>

Swift SVN r20931