swift234

fix <rdar://problem/16954239> Crash in type lowering when using bridged types but not foundation

by propagating the null bridging type up correctly.  The experience is now:

$ swift t.swift -emit-sil
<unknown>:0: error: could not find Objective-C bridge type for type 'ImplicitlyUnwrappedOptional<String>'; did you forget to import Foundation?
LLVM ERROR: unable to set up the ObjC bridge!

which is horrible, but consistent, and a lot less head-scratching than what we did before.

No testcase since this isn't a recoverable error and doesn't matter much.



Swift SVN r18356