message: fix build issue on gcc8
diff: @@ -46,6 +46,18 @@ SET(AVX512_VNNI_CODE "
  __m512i src3 = _mm512_set1_epi8(a3);
  // detect avx512_vnni
  _mm512_dpbusds_epi32(src3, src1, src2);
  +
  + // detect avx512
  + __m512i a = _mm512_set_epi8(0, 0, 0, 0, 0, 0, 0, 0,
  + 0, 0, 0, 0, 0, 0, 0, 0,
  + 0, 0, 0, 0, 0, 0, 0, 0,
  + 0, 0, 0, 0, 0, 0, 0, 0,
  + 0, 0, 0, 0, 0, 0, 0, 0,
  + 0, 0, 0, 0, 0, 0, 0, 0,
  + 0, 0, 0, 0, 0, 0, 0, 0,
  + 0, 0, 0, 0, 0, 0, 0, 0);
  + __m512i b = a;
  + __mmask64 equality_mask = _mm512_cmp_epi8_mask(a, b, _MM_CMPINT_EQ);
  return 0;
  }
  ")
  