Core/Game: Move singleton instances into compilation units

* Fixes issues when building shared libraries
  (prevents gcc and clang from providing several instance)

src/server/game/AI/SmartScripts/SmartScriptMgr.cpp

@@ -28,6 +28,12 @@
 
 #include "SmartScriptMgr.h"
 
+SmartWaypointMgr* SmartWaypointMgr::instance()
+{
+    static SmartWaypointMgr instance;
+    return &instance;
+}
+
 void SmartWaypointMgr::LoadFromDB()
 {
     uint32 oldMSTime = getMSTime();
@@ -99,6 +105,12 @@ SmartWaypointMgr::~SmartWaypointMgr()
     }
 }
 
+SmartAIMgr* SmartAIMgr::instance()
+{
+    static SmartAIMgr instance;
+    return &instance;
+}
+
 void SmartAIMgr::LoadSmartAIFromDB()
 {
     LoadHelperStores();