Properly link flecs library

engine/libs/flecs/examples/cpp/relationships/basics/src/main.cpp

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+#include <basics.h>
+#include <iostream>
+
+// Type used for Eats relationship
+struct Eats { };
+
+int main(int, char*[]) {
+    flecs::world ecs;
+
+    // Entity used for Grows relationship
+    flecs::entity grows = ecs.entity("Grows");
+
+    // Relationship objects
+    flecs::entity apples = ecs.entity("Apples");
+    flecs::entity pears = ecs.entity("Pears");
+
+    // Create an entity with 3 relationships. Relationships are like regular components,
+    // but combine two types/identifiers into an (relationship, object) pair.
+    flecs::entity bob = ecs.entity("Bob")
+        // Pairs can be constructed from a type and entity
+        .add<Eats>(apples)
+        .add<Eats>(pears)
+        // Pairs can also be constructed from two entity ids
+        .add(grows, pears);
+
+    // Has can be used with relationships as well
+    std::cout << "Bob eats apples? " << bob.has<Eats>(apples) << "\n";
+
+    // Wildcards can be used to match relationships
+    std::cout << "Bob grows food? " << bob.has(grows, flecs::Wildcard) << "\n";
+
+    // Print the type of the entity. Should output:
+    //   (Identifier,Name),(Eats,Apples),(Eats,Pears),(Grows,Pears)
+    std::cout << "Bob's type: [" << bob.type().str() << "]\n";
+
+    // Relationships can be iterated for an entity. This iterates (Eats, *):
+    bob.each<Eats>([](flecs::entity second) {
+        std::cout << "Bob eats " << second.name() << "\n";
+    });
+
+    // Iterate by explicitly providing the pair. This iterates (*, Pears):
+    bob.each(flecs::Wildcard, pears, [](flecs::id id) {
+        std::cout << "Bob " << id.first().name() << " pears\n";
+    });
+
+    // Get first target of relationship
+    std::cout << "Bob eats " << bob.target<Eats>().name() << "\n";
+
+    // Get second target of relationship
+    std::cout << "Bob also eats " << bob.target<Eats>(1).name() << "\n";
+}