A bunch of tests that technically require Objective-C interop were
not labeled as such, and worked in the absence of Objective-C interop
due to bugs in the type checker.
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
This condition is already checked from defineDefaultConstructor's only caller,
addImplicitConstructors, and the two conditions had drifted. This was causing
issues in the multi-file case, where the optionals hadn't been given an
explicit initial value yet.
rdar://problem/18716572
Swift SVN r23017