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
The @semantics attribute allows the stdlib to mark some functions as
having a specific semantics. The optimizer can use this information
to optimize the code.
Swift SVN r19328
