title: How to detect if constexpr is supported at compile time
body: <p>I am currently working in a project where we target several platforms and our codebase is built using several different compilers (gcc/clang/vc++).</p>
  
  <p>For our windows platform, we use VS2013 which currently does not support 'constexpr', and I was wondering if there is a way to check if this feature is supported beyond checking if we are in Windows and the version of the compiler is lower than VS2015.</p>
  
  <p>This way I could decide when to extend an existent type with compile-time generated members using template metaprogramming -involving usage of constexpr- only if this is available.</p>