Fix warnings from g++5 or higher (#1510)

dmlc-core

@@ -1 +1 @@
-Subproject commit d8d4dccb8bd89af9f57aa19e7523f0b755563ca4
+Subproject commit c5c33124d2cc4a30ce8409d881c945c5bb04d06e

include/xgboost/gbm.h

@@ -161,7 +161,8 @@ struct GradientBoosterReg
  * \endcode
  */
 #define XGBOOST_REGISTER_GBM(UniqueId, Name)                            \
-  static ::xgboost::GradientBoosterReg & __make_ ## GradientBoosterReg ## _ ## UniqueId ## __ = \
+  static DMLC_ATTRIBUTE_UNUSED ::xgboost::GradientBoosterReg &          \
+  __make_ ## GradientBoosterReg ## _ ## UniqueId ## __ =                \
       ::dmlc::Registry< ::xgboost::GradientBoosterReg>::Get()->__REGISTER__(Name)
 
 }  // namespace xgboost

include/xgboost/objective.h

@@ -105,7 +105,8 @@ struct ObjFunctionReg
  * \endcode
  */
 #define XGBOOST_REGISTER_OBJECTIVE(UniqueId, Name)                      \
-  static ::xgboost::ObjFunctionReg & __make_ ## ObjFunctionReg ## _ ## UniqueId ## __ = \
+  static DMLC_ATTRIBUTE_UNUSED ::xgboost::ObjFunctionReg &              \
+  __make_ ## ObjFunctionReg ## _ ## UniqueId ## __ =                    \
       ::dmlc::Registry< ::xgboost::ObjFunctionReg>::Get()->__REGISTER__(Name)
 }  // namespace xgboost
 #endif  // XGBOOST_OBJECTIVE_H_

include/xgboost/tree_updater.h

@@ -82,7 +82,8 @@ struct TreeUpdaterReg
  * \endcode
  */
 #define XGBOOST_REGISTER_TREE_UPDATER(UniqueId, Name)                   \
-  static ::xgboost::TreeUpdaterReg& __make_ ## TreeUpdaterReg ## _ ## UniqueId ## __ = \
+  static DMLC_ATTRIBUTE_UNUSED ::xgboost::TreeUpdaterReg&               \
+  __make_ ## TreeUpdaterReg ## _ ## UniqueId ## __ =                    \
       ::dmlc::Registry< ::xgboost::TreeUpdaterReg>::Get()->__REGISTER__(Name)
 
 }  // namespace xgboost

rabit

@@ -1 +1 @@
-Subproject commit 2dd7476ad7e4afe97eb579d39aab226ff74400a6
+Subproject commit a9a2a69dc1144180a43f7d2d1097264482be7817

src/c_api/c_api.cc

@@ -736,4 +736,4 @@ XGB_DLL int XGBoosterSaveRabitCheckpoint(BoosterHandle handle) {
 }
 
 // force link rabit
-static int XGBOOST_LINK_RABIT_C_API_ = RabitLinkTag();
+static DMLC_ATTRIBUTE_UNUSED int XGBOOST_LINK_RABIT_C_API_ = RabitLinkTag();