Properly link flecs library

engine/libs/flecs/test/custom_builds/cpp/snapshot/src/main.cpp

@@ -0,0 +1,10 @@
+#include <snapshot.h>
+#include <iostream>
+
+int main(int, char *[]) {
+    flecs::world world;
+
+    auto s = world.snapshot();
+
+    s.restore();
+}