unbreak NativeCall for the JVM

The call to nqp::buildnativecall fails because it does not recognize the first arg as
an NativeCallInstance. Doing the clone always like before e167669a498b91543144c7657e5cdb8d0cb40e65
makes it work, see also: https://gist.github.com/FROGGS/0d4b5c771c7d9eb4f5b6