VM: fixed an error introduced in the last merging

src/nasal_vm.h

@@ -320,15 +320,16 @@ public:
         flag_limited_mode = flag;
     }
 
+    auto get_gc_time_ms() const {
+        return ngc.get_gc_time_ms();
+    }
+
     void set_interrupt_ptr(std::atomic<bool>* p) {
         interrupt_ptr = p;
     }
 
 private:
     std::atomic<bool>* interrupt_ptr = nullptr;
-    auto get_gc_time_ms() const {
-        return ngc.get_gc_time_ms();
-    }
 };
 
 inline bool vm::boolify(const var& val) {