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
...unless the functions are declared [transparent], or if we're in an
immediate mode (in which case we won't get a separate chance to link
against the imported TUs).
This is an optimization that will matter more when we start dealing with
Xcode projects with many cross-file dependencies, especially if we have
some kind of implicit import of the other source files in the project.
In the future, we may want to parse more function bodies for the purpose
of inlining, not just the transparent ones, but we weren't taking
advantage of that now, so it's not a regression. (We're still not taking
advantage of it even for [transparent] functions.)
Swift SVN r7698
