Most tests were using %swift or similar substitutions, which did not
include the target triple and SDK. The driver was defaulting to the
host OS. Thus, we could not run the tests when the standard library was
not built for OS X.
Swift SVN r24504
Swift can infer associated types for decls conforming to protocols, but if
there's already an explicit member type available, we can just use that.
We could probably push this deeper (into qualified lookup), but this is
enough to avoid cases of accidental circular conformance checking, where
we need a particular member type to satisfy a parent conformance.
rdar://problem/18576085
Swift SVN r22664
