message: add inline to avoid duplicate symbols (discovered with misconfigured compute-device spec)
diff: // 'double' atomicAdd implementation for previous versions of CUDA
  #if defined(MFEM_USE_CUDA) && defined(__CUDA_ARCH__) && __CUDA_ARCH__ < 600
  -MFEM_DEVICE double atomicAdd(double *add, double val)
  +MFEM_DEVICE inline double atomicAdd(double *add, double val)
  {
  unsigned long long int *ptr = (unsigned long long int *) add;
  unsigned long long int old = *ptr, reg;
  