Use the ARM_THREAD_STATE32 flavor in the call to thread_get_state() when
running on 64-bit iOS 7+. If we don't iOS will assume we pass it an
arm_unified_thread_state_t while we actually pass it an arm_thread_state_t
which is a lot smaller. Without this fix thread_get_state() will corrupt the
stack and the app will crash.
Merge pull request #52 from robovm/thread_get_state_stack_corruption_on_ios_64bit

Use ARM_THREAD_STATE32 as flavor in call to thread_get_state (Darwin/AArch64)