fix(Core/Misc): all GCC warnings (#3457)

src/server/scripts/Outland/GruulsLair/instance_gruuls_lair.cpp

@@ -45,7 +45,7 @@ class instance_gruuls_lair : public InstanceMapScript
                 {
                     case NPC_MAULGAR:
                         _maulgarGUID = creature->GetGUID();
-                        // no break;
+                        [[fallthrough]];
                     case NPC_KROSH_FIREHAND:
                     case NPC_OLM_THE_SUMMONER:
                     case NPC_KIGGLER_THE_CRAZED:

src/server/scripts/Outland/zone_shattrath_city.cpp

@@ -508,7 +508,7 @@ public:
 
             _events.Update(diff);
 
-            switch (uint32 eventId = _events.ExecuteEvent())
+            switch (_events.ExecuteEvent())
             {
                 case EVENT_SPELL_ISHANAH_HOLY_SMITE:
                     me->CastSpell(me->GetVictim(), HOLY_SMITE_ISHANAH, false);