bc267dd729
* Use ptr from mmap for `GHistIndexMatrix` and `ColumnMatrix`. - Define a resource for holding various types of memory pointers. - Define ref vector for holding resources. - Swap the underlying resources for GHist and ColumnM. - Add documentation for current status. - s390x support is removed. It should work if you can compile XGBoost, all the old workaround code does is to get GCC to compile.