cmake DEAL_II_HAVE_SSE2 examples

dealii/dealii cmake/checks/check_01_cpu_features.cmake :78

CHECK_CXX_SOURCE_RUNS(
    "
    #include <x86intrin.h>
    int main()
    {
    __m128d a, b;
    const unsigned int vector_bytes = sizeof(__m128d);
    const int n_vectors = vector_bytes/sizeof(double);
    __m128d * data =
      reinterpret_cast<__m128d*>(_mm_malloc (2*vector_bytes, vector_bytes));
    double * ptr = reinterpret_cast<double*>(&a);
    ptr[0] = static_cast<volatile double>(1.0);
    for (int i=1; i<n_vectors; ++i)
      ptr[i] = 0.0;
    b = _mm_set1_pd (static_cast<volatile double>(2.25));
    data[0] = _mm_add_pd (a, b);
    data[1] = _mm_mul_pd (b, data[0]);
    ptr = reinterpret_cast<double*>(&data[1]);
    int return_value = 0;
    if (ptr[0] != 7.3125)
      return_value = 1;
    for (int i=1; i<n_vectors; ++i)
      if (ptr[i] != 5.0625)
        return_value = 1;
    _mm_free (data);
    return return_value;
    }
    "
    DEAL_II_HAVE_SSE2)

dealii/dealii cmake/checks/check_01_cpu_features.cmake :316

elseif(DEAL_II_HAVE_SSE2)