Fix deadlock while attaching to inferiors

Summary:
There was a race condition in the AsyncThread, where we would end up sending a vAttach
notification to the thread before it got a chance set up its listener (this can be reproduced by
adding a sleep() at the very beginning of ProcessGDBRemote::AsyncThread()). This event would then
get lost and we LLDB would deadlock. I fix this by setting up the listener early on, in the
ProcessGDBRemote constructor.

This should improve the stability of all attach tests. For now, I am removing XTIMEOUT from
TestAttachResume, and will watch the buildbots for signs of trouble.

Reviewers: clayborg, ovyalov

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D12552

llvm-svn: 246756
diff --git a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h
index 0048004..c3b201b 100644
--- a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h
+++ b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h
@@ -358,6 +358,7 @@
     Mutex m_last_stop_packet_mutex;
     GDBRemoteDynamicRegisterInfo m_register_info;
     Broadcaster m_async_broadcaster;
+    Listener m_async_listener;
     HostThread m_async_thread;
     Mutex m_async_thread_state_mutex;
     typedef std::vector<lldb::tid_t> tid_collection;