Clean up C++ warnings (#6213)

include/xgboost/gbm.h

@@ -75,8 +75,9 @@ class GradientBooster : public Model, public Configurable {
    * \param prediction The output prediction cache entry that needs to be updated.
    * the booster may change content of gpair
    */
-  virtual void DoBoost(DMatrix* p_fmat, HostDeviceVector<GradientPair>* in_gpair,
-                       PredictionCacheEntry *prediction) = 0;
+  virtual void DoBoost(DMatrix* p_fmat,
+                       HostDeviceVector<GradientPair>* in_gpair,
+                       PredictionCacheEntry*) = 0;
 
   /*!
    * \brief generate predictions for given feature matrix
@@ -103,10 +104,10 @@ class GradientBooster : public Model, public Configurable {
    * \param           layer_begin (Optional) Begining of boosted tree layer used for prediction.
    * \param           layer_end   (Optional) End of booster layer. 0 means do not limit trees.
    */
-  virtual void InplacePredict(dmlc::any const &x, float missing,
-                              PredictionCacheEntry *out_preds,
-                              uint32_t layer_begin = 0,
-                              uint32_t layer_end = 0) const {
+  virtual void InplacePredict(dmlc::any const &, float,
+                              PredictionCacheEntry*,
+                              uint32_t,
+                              uint32_t) const {
     LOG(FATAL) << "Inplace predict is not supported by current booster.";
   }
   /*!

include/xgboost/metric.h

@@ -41,14 +41,14 @@ class Metric : public Configurable {
    * override this function to maintain internal configuration
    * \param in JSON object containing the configuration
    */
-  void LoadConfig(Json const& in) override {}
+  void LoadConfig(Json const&) override {}
   /*!
    * \brief Save configuration to JSON object
    * By default, metric has no internal configuration;
    * override this function to maintain internal configuration
    * \param out pointer to output JSON object
    */
-  void SaveConfig(Json* out) const override {}
+  void SaveConfig(Json*) const override {}
 
   /*!
    * \brief evaluate a specific metric

include/xgboost/objective.h

@@ -53,7 +53,7 @@ class ObjFunction : public Configurable {
    * \brief transform prediction values, this is only called when Prediction is called
    * \param io_preds prediction values, saves to this vector as well
    */
-  virtual void PredTransform(HostDeviceVector<bst_float> *io_preds) {}
+  virtual void PredTransform(HostDeviceVector<bst_float>*) {}
 
   /*!
    * \brief transform prediction values, this is only called when Eval is called,