Properly link flecs library

engine/libs/flecs/examples/c/relationships/symmetric_relations/src/main.c

@@ -0,0 +1,32 @@
+#include <symmetric_relations.h>
+#include <stdio.h>
+
+int main(int argc, char *argv[]) {
+    ecs_world_t *ecs = ecs_init_w_args(argc, argv);
+
+    ECS_TAG(ecs, TradesWith);
+
+    // Register TradesWith as symmetric relationship. Symmetric relationships
+    // go both ways, adding (R, B) to A will also add (R, A) to B.
+    ecs_add_id(ecs, TradesWith, EcsSymmetric);
+
+    // Create two players
+    ecs_entity_t player_1 = ecs_new_id(ecs);
+    ecs_entity_t player_2 = ecs_new_id(ecs);
+
+    // Add (TradesWith, player_2) to player_1. This also adds 
+    // (TradesWith, player_1) to player_2.
+    ecs_add_pair(ecs, player_1, TradesWith, player_2);
+
+    // Log platoon of unit
+    printf("Player 1 trades with Player 2: %s\n",
+        (ecs_has_pair(ecs, player_1, TradesWith, player_2) ? "true" : "false"));
+    printf("Player 2 trades with Player 1: %s\n",
+        (ecs_has_pair(ecs, player_2, TradesWith, player_1) ? "true" : "false"));
+
+    // Output:
+    //  Player 1 trades with Player 2: true
+    //  Player 2 trades with Player 1: true
+
+    return ecs_fini(ecs);
+}