Properly link flecs library

engine/libs/flecs/examples/cpp/prefabs/variant/src/main.cpp

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+#include <variant.h>
+#include <iostream>
+
+/* Prefabs can inherit from each other, which creates prefab variants. With
+ * variants applications can reuse a commmon set of components and specialize it
+ * by adding or overriding components on the variant. */
+
+struct Attack { 
+    double value; 
+};
+
+struct Defense { 
+    double value; 
+};
+
+struct FreightCapacity { 
+    double value; 
+};
+
+struct ImpulseSpeed { 
+    double value; 
+};
+
+struct Position { 
+    double x;
+    double y;
+};
+
+int main() {
+    flecs::world ecs;
+
+    // Create a base prefab for SpaceShips.
+    flecs::entity SpaceShip = ecs.prefab("SpaceShip")
+        .set<ImpulseSpeed>({ 50 })
+        .set<Defense>({ 25 });
+
+        // Create a Freighter variant which inherits from SpaceShip
+        flecs::entity Freighter = ecs.prefab("Freighter")
+            .is_a(SpaceShip)
+            .set<FreightCapacity>({ 100 })
+            .set<Defense>({ 50 });
+
+            // Create a MammotFreighter variant which inherits from Freighter
+            flecs::entity MammothFreighter = ecs.prefab("MammothFreighter")
+                .is_a(Freighter)
+                .set<FreightCapacity>({ 500 });
+
+        // Create a Frigate variant which inherits from SpaceShip
+        ecs.prefab("Frigate")
+            .is_a(SpaceShip)
+            .set<Attack>({ 100 })
+            .set<Defense>({ 75 })
+            .set<ImpulseSpeed>({ 125 });
+
+    // Create an instance of the MammothFreighter. This entity will inherit the
+    // ImpulseSpeed from SpaceShip, Defense from Freighter and FreightCapacity
+    // from MammothFreighter.
+    flecs::entity inst = ecs.entity("my_freighter").is_a(MammothFreighter);
+
+    // Add a private Position component.
+    inst.set<Position>({ 10, 20});
+
+    // Instances can override inherited components to give them a private copy
+    // of the component. This freighter got an armor upgrade:
+    inst.set<Defense>({ 100 });
+
+    // Queries can match components from multiple levels of inheritance
+    ecs.each([](flecs::entity e, 
+        Position& p, ImpulseSpeed& s, Defense& d, FreightCapacity& c) {
+            std::cout << e.name() << ":\n";
+            std::cout << " - position: " << p.x << ", " << p.y << "\n";
+            std::cout << " - impulse speed: " << s.value << "\n";
+            std::cout << " - defense: " << d.value << "\n";
+            std::cout << " - capacity: " << c.value << "\n";
+        });
+
+    // Output:
+    //   my_freighter:
+    //    - position: 10, 20
+    //    - impulse speed: 50
+    //    - defense: 100
+    //    - capacity: 500
+}