Avoid the race condition Stephen Wilson was worried about in revision 123465...

Avoid the race condition Stephen Wilson was worried about in revision 123465 by making a local copy. We need to be able to have the private state thread let the lldb_private::Process class that it has exited, otherwise we end up with a timeout when the process destructor or DoDestroy is called where the private state thread has already exited and then StopPrivateStateThread() will wait for the thread which has already existed to respond to it. 

llvm-svn: 124038