More generally, an unavailable initializer shouldn't stomp on an
available initializer, because it's possible that (for example) a
designated initializer will be unavailable but a factory initializer
will be available, so one still construct objects of that type.
Fixes rdar://problem/26238032.
It's possible for swift_name to make a global declaration into a
member of another entity that has not been seen yet. In such cases,
delay resolution until the end of the translation unit (module). Fixes
the rest of rdar://problem/25502497.
Some of the callers to importDeclContextOf could and should have
passed an effective context, but didn't, so (e.g.) an enum defined in
C couldn't be mapped to a nested type in Swift. Eliminate the
single-argument importDeclContextOf honeypot so we remember to pass
down the effective Clang context. Fixes rdar://problem/25502497.
