8210861: Move assert to help diagnose rare RedefineStress crash

Assert that Method being marked on stack hasn't been missed by previous metadata walk

Reviewed-by: lfoltan

src/hotspot/share/oops/method.cpp

@@ -2152,6 +2152,8 @@ void Method::set_on_stack(const bool value) {
   if (value && !already_set) {
     MetadataOnStackMark::record(this);
   }
+  assert(!value || !is_old() || is_obsolete() || is_running_emcp(),
+         "emcp methods cannot run after emcp bit is cleared");
 }
 
 // Called when the class loader is unloaded to make all methods weak.