title: Xcode 4.5 and C++11 headers not found
body: <p>For example, if I include 'chrono' or 'type_traits' it fails to find header and gives me an error, but if I use lamdas or auto/decltype it compiles fine. I am using Xcode 4.5.1  with the flags,  C++ Language Dialect=C++11[-std=c++11] and C++ Standard Library = libc++[LLVM C++ standard library with C++11 support]</p>
  
  <p>Any help on why the newer header file isn't being found?</p>