Fix lock hierarchy violation in Process (lock ordering of ThreadList mutex and StackFrameList mutex)

- this fix ensures the ThreadList mutex is always locked before the StackFrameList mutex

Situation where deadlock could occur (without this fix):
Thread 1 is in Process::WillResume and locks the ThreadList mutex (on entry), and subsequently calls StackFrameList::Clear() which locks the StackFrameList mutex.
Meanwhile, thread 2 is in Process::RunThreadPlan and calls Thread::SetSelectedFrame() (which locks the StackFrameList mutex) before calling GetSelectedThread (which attempts to lock the ThreadList mutex)

In my testing on both Linux and Mac OS X, I was unable to reproduce any hangs with this patch applied.

llvm-svn: 187522

lldb/source/Target/Process.cpp

@@ -5418,6 +5418,7 @@ Process::RunThreadPlan (ExecutionContext &exe_ctx,
             if (GetThreadList().SetSelectedThreadByIndexID (selected_tid) && selected_stack_id.IsValid())
             {
                 // We were able to restore the selected thread, now restore the frame:
+                Mutex::Locker lock(GetThreadList().GetMutex());
                 StackFrameSP old_frame_sp = GetThreadList().GetSelectedThread()->GetFrameWithStackID(selected_stack_id);
                 if (old_frame_sp)
                     GetThreadList().GetSelectedThread()->SetSelectedFrame(old_frame_sp.get());