Fix CRAN check warnings/notes (#3988)

* fix

* reorder declaration to match initialization

src/common/transform.h

@@ -172,8 +172,8 @@ class Transform {
     /*! \brief Range object specifying parallel threads index range. */
     Range range_;
     /*! \brief Whether resharding for vectors is required. */
-    bool reshard_;
     GPUDistribution distribution_;
+    bool reshard_;
   };
 
  public: