title: ‘is_trivially_copyable’ is not a member of ‘std’
body: <p>My gcc version is 4.8.3 20140624. I can use <code>is_pod</code>, <code>is_trivial</code>, <code>is_standard_layout</code>, but fail when trying <code>is_trivially_copyable</code>, <code>is_constructible</code> and <code>is_default_constructible</code>, maybe more. The error message is <code>'xxx' is not a member of 'std'</code>.</p>
  
  <p>What's the problem here? Are they even supported by the current GCC? Thanks!</p>