Unreachable code in nmethod.cpp inside #ifdef DEBUG

HotSpot doesn't define the DEBUG macro, so the assert assert_lock_strong call is not included even in a debug build.

The code should be changed to #ifdef ASSERT instead.

bool nmethod::try_transition(int new_state_int) {
  signed char new_state = new_state_int;
#ifdef DEBUG
  if (new_state != unloaded) {
    assert_lock_strong(CompiledMethod_lock);
  }
#endif