Setting CXXFLAGS for Xcode project

ALL,

I'm trying to compile my program on OSX using Xcode 5.1.1. I did find where to set C++11 kind, but now I need to set "-std=libc++". Otherwise I'm getting compilation errors.

Could someone please help?

Thank you.

[EDIT]

The error received is

type_traits: file not found

[/EDIT]