Fix typo in GetAvailableSDKsInfo
Set simulator environment provided by CoreSimulator when running logic tests.

In Xcode 6 `sim` doesn't set `CFFIXED_USER_HOME` if simulator is not launched but this environment is used, for example, by NSHomeDirectory().
To avoid similar situations in future let's set all simulator environments provided by CoreSimulator framework before running logic tests.
Merge latest clang-as-ios-dylib changes.
Merge pull request #414 from facebook/nekto/clang_update

Merge latest clang-as-ios-dylib changes.
Fix issue with dispatch thread soft limit to avoid potential deadlock.

Though it is not documented but apparently there is dispatch thread soft limit on OS X (and iOS) which is equal to 64. Generation of more then 64 threads could lead to error like this: `Dispatch Thread Soft Limit: 64 reached in 2244 of 2244 samples -- too many dispatch threads blocked in synchronous operations`.

In xctool it is a semaphore which limits number of currently running threads (`jobLimiter`) which value is equal to `[[NSProcessInfo processInfo] processorCount]`. But the problem is that it doesn't limit number of created threads which could easily be more then 64. Everything would be fine if generated threads don't create other threads but it could easily happen when interaction with CoreSimulator framework happens.

So there could be a situation when there is 64 threads created to run logic tests, and every thread wants to access something in CoreSimulator frameworks which tries to dispatch another thread to guard access to shared resources but fails (locks) because there is a 64 dispatch thread soft limit. At that point all threads will be deadlocked.
Merge pull request #409 from facebook/nekto/fix_dispatch_limit

Fix issue with dispatch thread soft limit to avoid potential deadlock.
Merge pull request #410 from facebook/nekto/set_sim_envs

Set simulator environment provided by CoreSimulator when running logic tests.
Append xcodebuild version to xctool build output directory.

After Xcode 6 support was added several macros were introduced to simplify switching between Xcode 5 and Xcode 6 implementations. These macros cause different runtime issues after switching from Xcode 5 to 6 or back that are hard to debug.
Let's improve build scripts so builds for different versions of xcodebuild are saved in different directories.