cmake DEAL_II_HAVE_ATTRIBUTE_FALLTHROUGH examples

dealii/dealii cmake/checks/check_01_cxx_features.cmake :536 

CHECK_CXX_SOURCE_COMPILES(
  "
  int main()
  {
    int i = 42;
    int j = 10;
    switch(i)
      {
      case 1:
        ++j;
        __attribute__((fallthrough));
      case 2:
        ++j;
        __attribute__((fallthrough));
      default:
        break;
      }
  }
  "
  DEAL_II_HAVE_ATTRIBUTE_FALLTHROUGH
  )

dealii/dealii cmake/checks/check_01_cxx_features.cmake :560 

elseif(DEAL_II_HAVE_ATTRIBUTE_FALLTHROUGH)