message: add 64bit check for superlu
diff: #include "superlu_defs.h"
  #include "superlu_ddefs.h"
  +#if XSDK_INDEX_SIZE == 64
  +#error "SuperLUDist has been built with 64bit integers. This is not supported"
  +#endif
  +
  using namespace std;
  namespace mfem
  