Remote Non-Stop Support

Summary:
 
This patch is the beginnings of support for Non-stop mode in the remote protocol. Letting a user examine stopped threads, while other threads execute freely.

Non-stop mode is enabled using the setting target.non-stop-mode, which sends a QNonStop packet when establishing the remote connection.
Changes are also made to treat the '?' stop reply packet differently in non-stop mode, according to spec https://sourceware.org/gdb/current/onlinedocs/gdb/Remote-Non_002dStop.html#Remote-Non_002dStop.
A setting for querying the remote for default thread on setup is also included.

Handling of '%' async notification packets will be added next.

Reviewers: clayborg

Subscribers: lldb-commits, ADodds, ted, deepak2427

Differential Revision: http://reviews.llvm.org/D9656

llvm-svn: 237239

lldb/source/Utility/StringExtractorGDBRemote.cpp

@@ -64,6 +64,10 @@ StringExtractorGDBRemote::GetServerPacketType () const
     const char *packet_cstr = m_packet.c_str();
     switch (m_packet[0])
     {
+
+    case '%':
+        return eServerPacketType_notify;
+
     case '\x03':
         if (packet_size == 1) return eServerPacketType_interrupt;
         break;