Properly link flecs library

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

@@ -0,0 +1,39 @@
+#include <systems.h>
+#include <iostream>
+
+struct Position { 
+    double x, y;
+};
+
+struct Velocity { 
+    double x, y;
+};
+
+int main(int, char *[]) {
+    flecs::world ecs;
+
+    // Create a system for Position, Velocity. Systems are like queries (see
+    // queries) with a function that can be ran or scheduled (see pipeline).
+    flecs::system s = ecs.system<Position, const Velocity>()
+        .each([](flecs::entity e, Position& p, const Velocity& v) {
+            p.x += v.x;
+            p.y += v.y;
+            std::cout << e.name() << ": {" << p.x << ", " << p.y << "}\n";
+        });
+
+    // Create a few test entities for a Position, Velocity query
+    ecs.entity("e1")
+        .set<Position>({10, 20})
+        .set<Velocity>({1, 2});
+
+    ecs.entity("e2")
+        .set<Position>({10, 20})
+        .set<Velocity>({3, 4});
+
+    // This entity will not match as it does not have Position, Velocity
+    ecs.entity("e3")
+        .set<Position>({10, 20});
+
+    // Run the system
+    s.run();
+}