Properly link flecs library

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

@@ -0,0 +1,38 @@
+#include <time_interval.h>
+#include <iostream>
+
+// This example shows how to run a system at a specified time interval.
+
+void Tick(flecs::iter& it) {
+    std::cout << it.system().name() << "\n";
+}
+
+int main(int, char *[]) {
+    flecs::world ecs;
+
+    ecs.system("Tick")
+        .interval(1.0) // time in seconds
+        .iter(Tick);
+
+    ecs.system("FastTick")
+        .interval(0.5)
+        .iter(Tick);
+
+    // Run the main loop at 60 FPS
+    ecs.set_target_fps(60);
+
+    while (ecs.progress()) { }
+
+    // Output
+    //  FastTick
+    //  Tick
+    //  FastTick
+    //  FastTick
+    //  Tick
+    //  FastTick
+    //  FastTick
+    //  Tick
+    //  FastTick
+    //  FastTick
+    //  ...
+}