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
(This could occur, for instance, via a forward reference to a member defined in an extension to a generic type.) This problem has been popping up a lot lately, and
was making some of the recent runtime work difficult. (rdar://problem/16481483)
Swift SVN r15805
