message: Fixed
  Cherrypicking the eigen fix to XACC:
  Updating the whole eigen to the latest version brings other unneccesary compatibility issue.
diff: @@ -452,7 +452,7 @@ template<> EIGEN_STRONG_INLINE Packet4f pandnot<Packet4f>(const Packet4f& a, con
  template<> EIGEN_STRONG_INLINE Packet4i pandnot<Packet4i>(const Packet4i& a, const Packet4i& b) { return vec_and(a, vec_nor(b, b)); }
  template<> EIGEN_STRONG_INLINE Packet4f pselect(const Packet4f& mask, const Packet4f& a, const Packet4f& b) {
  - return vec_sel(b, a, mask);
  + return vec_sel(b, a, reinterpret_cast<Packet4ui>(mask));
  }
  template<> EIGEN_STRONG_INLINE Packet4f pround<Packet4f>(const Packet4f& a) { return vec_round(a); }
  