Properly link flecs library

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

@@ -0,0 +1,31 @@
+#include <delta_time.h>
+#include <stdio.h>
+
+void PrintDeltaTime(ecs_iter_t *it) {
+    // Print delta_time. The same value is passed to all systems.
+    printf("delta_time: %f\n", (double)it->delta_time);
+}
+
+int main(int argc, char *argv[]) {
+    ecs_world_t *ecs = ecs_init_w_args(argc, argv);
+
+    // 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(ecs, PrintDeltaTime, EcsOnUpdate, 0);
+
+    // 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(ecs, 0.0f);
+
+    // The following calls should print a delta_time of approximately 100ms
+
+    ecs_os_sleep(0, 100 * 1000 * 1000);
+    ecs_progress(ecs, 0.0f);
+
+    ecs_os_sleep(0, 100 * 1000 * 1000);
+    ecs_progress(ecs, 0.0f);
+
+    return ecs_fini(ecs);
+}