#include <AvailabilityMacros.h> if you want to use them.  This was causing us to skip
the code that should have set thread names on Mac OS X.

<rdar://problem/15517264>


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@195403 91177308-0d34-0410-b5e6-96231b3b80d8