Fix a race on process exit

[labath]

Summary

Process::SetExitStatus was popping the process io handler and resetting m_process_input_reader
shared pointer, which is not a safe thing to do as the function is called asynchronously and
other threads may be accessing the member variable. (E.g. if the process terminates really
quickly, the private state thread might only be in the process of pushing the handler on the
stack. Sometimes, this leads to deadlock, as the shared pointer's state gets corrupted by the
concurrent access.

Since the IOHandler will be popped anyway in Process:HandleProcessStateChangedEvent when the
exited event gets processed, doing the same in SetExitStatus seems to be unnecessary.

[clayborg]

Looks good.

lldb/trunk/source/Target/Process.cpp

Process::SetExitStatus (int status, const char *cstr)
     }
 
     m_exit_status = status;
     if (cstr)
         m_exit_string = cstr;
     else
         m_exit_string.clear();
 
-    // When we exit, we don't need the input reader anymore
-    if (m_process_input_reader)
-    {
-        m_process_input_reader->SetIsDone(true);
-        m_process_input_reader->Cancel();
-        m_process_input_reader.reset();
-    }
-
     // Clear the last natural stop ID since it has a strong
     // reference to this process
     m_mod_id.SetStopEventForLastNaturalStopID(EventSP());
 
     SetPrivateState (eStateExited);
 
     // Allow subclasses to do some cleanup
     DidExit ();