Properly link flecs library

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

@@ -0,0 +1,33 @@
+#include <target_fps.h>
+#include <iostream>
+
+int main(int, char *[]) {
+    flecs::world ecs;
+
+    // Create system that prints delta_time. This system doesn't query for any
+    // components which means it won't match any entities, but will still be ran
+    // once for each call to ecs_progress.
+    ecs.system()
+        .iter([](flecs::iter& it) {
+            std::cout << "delta_time: " << it.delta_time() << std::endl;
+        });
+
+    // Set target FPS to 1 frame per second
+    ecs.set_target_fps(1);
+
+    // Run 5 frames
+    for (int i = 0; i < 5; i ++) {
+        // To make sure the frame doesn't run faster than the specified target
+        // FPS ecs_progress will insert a sleep if the measured delta_time is
+        // smaller than 1 / target_fps.
+        //
+        // By default ecs_progress uses the sleep function provided by the OS
+        // which is not always very accurate. If more accuracy is required the
+        // sleep function of the OS API can be overridden with a custom one.
+        //
+        // If a value other than 0 is provided to the delta_time argument of
+        // ecs_progress, this value will be used to calculate the length of
+        // the sleep to insert.
+        ecs.progress();
+    }
+}