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
We still get things pretty wrong when the wrong module is found because
of a case-insensitive filesystem, but we can deal with that later.
<rdar://problem/15632996>
Swift SVN r12608
