Properly link flecs library

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

@@ -0,0 +1,27 @@
+#include <hierarchy.h>
+#include <iostream>
+
+// When a prefab has children, they are instantiated for an instance when the
+// IsA relationship to the prefab is added.
+
+int main() {
+    flecs::world ecs;
+
+    // Create a prefab hierarchy.
+    flecs::entity SpaceShip = ecs.prefab("SpaceShip");
+        ecs.prefab("Engine").child_of(SpaceShip);
+        ecs.prefab("Cockpit").child_of(SpaceShip);
+
+    // Instantiate the prefab. This also creates an Engine and Cockpit child
+    // for the instance.
+    flecs::entity inst = ecs.entity("my_spaceship").is_a(SpaceShip);
+    flecs::entity inst_engine = inst.lookup("Engine");
+    flecs::entity inst_cockpit = inst.lookup("Cockpit");
+
+    std::cout << "instance engine:  " << inst_engine.path() << "\n";
+    std::cout << "instance cockpit: " << inst_cockpit.path() << "\n";
+
+    // Output:
+    //   instance engine:  ::my_spaceship::Engine
+    //   instance cockpit: ::my_spaceship::Cockpit
+}