message: AVX 512 detection: workaround for older GCC
diff: #if defined __AVX512__ || defined __AVX512F__
  #include <immintrin.h>
  +
  +// Workaround for problem with GCC 5-6 in -O0 mode
  +struct v_uint32x16
  +{
  + __m512i val;
  + explicit v_uint32x16(__m512i v) : val(v) {}
  +};
  +inline v_uint32x16 operator << (const v_uint32x16& a, int imm)
  +{
  + return v_uint32x16(_mm512_slli_epi32(a.val, imm));
  +}
  +
  void test()
  {
  __m512i zmm = _mm512_setzero_si512();
  @@ -7,10 +19,13 @@ void test()
  __m256i b = _mm256_abs_epi64(a); // VL
  __m512i c = _mm512_abs_epi8(zmm); // BW
  __m512i d = _mm512_broadcast_i32x8(b); // DQ
  + v_uint32x16 e(d); e = e << 10;
  + __m512i f = _mm512_packus_epi32(d,d);
  #if defined __GNUC__ && defined __x86_64__
  asm volatile ("" : : : "zmm16", "zmm17", "zmm18", "zmm19");
  #endif
  }
  +
  #else
  #error "AVX512-SKX is not supported"
  #endif
  