[C++] Do not delete Var twice
diff --git a/main.cc b/main.cc
index 5a0c9fe..7081037 100644
--- a/main.cc
+++ b/main.cc
@@ -207,6 +207,8 @@
   for (Stmt* stmt : bootstrap_asts)
     delete stmt;
   delete ev;
+  // Each Var will be deleted by |ev|.
+  vars->clear();
   delete vars;
   delete cache_mgr;