2.3.1 build fails when HAVE_MPI is undefined, but HAVE_ARMCI is defined

It can't find ShmMessageGrp in the lines
```
#if defined(HAVE_ARMCI)
  else if (msg->class_desc() == ::class_desc<MPIMessageGrp>()) {
      default_memorygrp = new ARMCIMemoryGrp(msg);
      return default_memorygrp.pointer();
    }
#endif
```
because mpi is included only when HAVE_MPI is defined.