message: Alternative definition for unary minus with AVX512 when AVX512DQ is
  not available.
diff: @@ -112,7 +112,15 @@ template <> struct AutoSIMD<double,8,64>
  inline MFEM_ALWAYS_INLINE AutoSIMD operator-() const
  {
  AutoSIMD r;
  +#ifdef __AVX512DQ__
  r.m512d = _mm512_xor_pd(_mm512_set1_pd(-0.0), m512d);
  +#else
  + // Derived from https://github.com/vectorclass/version2
  + r.m512d = _mm512_castsi512_pd(
  + _mm512_xor_epi32(
  + _mm512_castpd_si512(m512d),
  + _mm512_set1_epi64(0x8000000000000000)));
  +#endif
  return r;
  }
  