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
When loading a module, we now try to load its dependencies as well.
If one of those dependencies can't be loaded, we emit an error message.
Swift SVN r5796