message: brush up AVX optimization in popcount
  - make sure SIMD optimization works even when AVX is not available
diff: @@ -4261,7 +4261,9 @@ int normHamming(const uchar* a, int n)
  _r0 = _mm256_add_epi32(_r0, _mm256_shuffle_epi32(_r0, 2));
  result = _mm256_extract_epi32_(_mm256_add_epi32(_r0, _mm256_permute2x128_si256(_r0, _r0, 1)), 0);
  }
  -#elif CV_POPCNT
  +#endif // CV_AVX2
  +
  +#if CV_POPCNT
  if(checkHardwareSupport(CV_CPU_POPCNT))
  {
  # if defined CV_POPCNT_U64
  @@ -4275,7 +4277,9 @@ int normHamming(const uchar* a, int n)
  result += CV_POPCNT_U32(*(uint*)(a + i));
  }
  }
  -#elif CV_SIMD128
  +#endif // CV_POPCNT
  +
  +#if CV_SIMD128
  if(hasSIMD128())
  {
  v_uint32x4 t = v_setzero_u32();
  @@ -4283,9 +4287,10 @@ int normHamming(const uchar* a, int n)
  {
  t += v_popcount(v_load(a + i));
  }
  - result = v_reduce_sum(t);
  + result += v_reduce_sum(t);
  }
  -#endif
  +#endif // CV_SIMD128
  +
  for(; i <= n - 4; i += 4)
  {
  result += popCountTable[a[i]] + popCountTable[a[i+1]] +
  @@ -4327,7 +4332,9 @@ int normHamming(const uchar* a, const uchar* b, int n)
  _r0 = _mm256_add_epi32(_r0, _mm256_shuffle_epi32(_r0, 2));
  result = _mm256_extract_epi32_(_mm256_add_epi32(_r0, _mm256_permute2x128_si256(_r0, _r0, 1)), 0);
  }
  -#elif CV_POPCNT
  +#endif // CV_AVX2
  +
  +#if CV_POPCNT
  if(checkHardwareSupport(CV_CPU_POPCNT))
  {
  # if defined CV_POPCNT_U64
  @@ -4341,7 +4348,9 @@ int normHamming(const uchar* a, const uchar* b, int n)
  result += CV_POPCNT_U32(*(uint*)(a + i) ^ *(uint*)(b + i));
  }
  }
  -#elif CV_SIMD128
  +#endif // CV_POPCNT
  +
  +#if CV_SIMD128
  if(hasSIMD128())
  {
  v_uint32x4 t = v_setzero_u32();
  @@ -4349,9 +4358,10 @@ int normHamming(const uchar* a, const uchar* b, int n)
  {
  t += v_popcount(v_load(a + i) ^ v_load(b + i));
  }
  - result = v_reduce_sum(t);
  + result += v_reduce_sum(t);
  }
  -#endif
  +#endif // CV_SIMD128
  +
  for(; i <= n - 4; i += 4)
  {
  result += popCountTable[a[i] ^ b[i]] + popCountTable[a[i+1] ^ b[i+1]] +
  