Properly link flecs library

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

@@ -0,0 +1,27 @@
+#include <delta_time.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;
+        });
+
+    // Call progress with 0.0f for the delta_time parameter. This will cause
+    // ecs_progress to measure the time passed since the last frame. The
+    // delta_time of the first frame is a best guess (16ms).
+    ecs.progress();
+
+    // The following calls should print a delta_time of approximately 100ms
+
+    ecs_os_sleep(0, 100 * 1000 * 1000);
+    ecs.progress();
+
+    ecs_os_sleep(0, 100 * 1000 * 1000);
+    ecs.progress();
+}