Tests importing AppKit have a tendency to be flaky when they share a
module cache with other builds using a different set of framework search
flags. Make sure they use a local cache, otherwise the compiler can
reuse incompatible cached modules.
Alternatively, we could align all builds using the same cache to have
exactly the same framework search paths or enable explicit module
builds. I picked the module cache as it's the most reliable solution in
the short and long term.
rdar://142949965
* Add --tvos option to swift-ios-test utility
* Mark failing tests appropriately
* Add support for TVOS predicates to stdlib unit tests
<rdar://problem/19854476> Swift: TV OS Testing Support
Swift SVN r28543
