MPI_ORDER_FORTRAN for MPI subarrays

[cwpearson]

Some interest in supporting MPI_ORDER_FORTRAN in MPI_Type_create_subarray calls from the Exascale Computing Project.

[cwpearson]

First modifications will principally happen here:

tempi/src/internal/types.cpp

Lines 257 to 283 in fe16ae7

	if (order != MPI_ORDER_C) {
	LOG_ERROR("unhandled order in subarray type");
	return Type();
	}
	MPI_Datatype oldtype = datatypes[0];
	MPI_Aint oldLb, oldExtent;
	int oldSize;
	MPI_Type_get_extent(oldtype, &oldLb, &oldExtent);
	MPI_Type_size(oldtype, &oldSize);
	for (int i = 0; i < ndims; ++i) {
	// int size = integers[1 + ndims * 0 + i];
	int subsize = integers[1 + ndims * 1 + i]; // subsize[i]
	int start = integers[1 + ndims * 2 + i];
	StreamData data{};
	data.off = start * oldExtent;
	data.stride = oldExtent;
	for (int j = i + 1; j < ndims; ++j) {
	data.stride *= integers[1 + ndims * 0 + j]; // size[j]
	data.off *= integers[1 + ndims * 0 + j]; // size[j]
	}
	data.count = subsize;
	datas.push_back(data);
	}
	std::reverse(datas.begin(), datas.end());