#include chrono fails in Xcode

I’ve a project (UE4.5, Xcode 6.0.1) where, in a C++ file, I’ve a simple:

#include <chrono>

Building fails with this message:

'chrono' file not found

I tried playing with the Xcode project settings, but I did’t found a solution.

Problem is related to UBT: IOSToolChain.cs does not include settings needed to enable full C++11 under iOS; opened C++11 not enabled for iOS - Mobile - Unreal Engine Forums .