message: Try cmath to get M_PI on WIN32
diff: #ifndef MFEM_BLAS_HPP
  #define MFEM_BLAS_HPP
  -#ifdef _WIN32
  -#define M_PI 3.14159265358979323846
  -#endif
  -
  #include "../config/config.hpp"
  +#include <cmath>
  #include "../general/globals.hpp"
  #include "../general/forall.hpp"
  #include "matrix.hpp"
  