This is the new and improved version of
__attribute__((annotate("swift1_unavailable"))), with the "improved" being
specifically that the 'availability' attribute supports a message.
This requires a corresponding Clang commit.
Swift side of rdar://problem/18768673.
Swift SVN r27053
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
