Handle O reply packets during qRcmd

Summary:
Gdb servers like openocd may send many $O reply packets for the client to output during a qRcmd command sequence.  Currently, lldb interprets the first O packet as an unexpected response.  Besides generating no output, this causes lldb to get out of sync with future commands because it continues reading O packets from the first command as response to subsequent commands.

This patch handles any O packets during an qRcmd, treating the first non-O packet as the true response.

Preliminary discussion at http://lists.llvm.org/pipermail/lldb-dev/2018-January/013078.html

Reviewers: clayborg

Reviewed By: clayborg

Subscribers: labath, lldb-commits

Differential Revision: https://reviews.llvm.org/D41745
Patch by Owen Shaw <llvm@owenpshaw.net>

llvm-svn: 322190
diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.cpp
index 18d9631..dd57dd1 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.cpp
@@ -275,6 +275,23 @@
 }
 
 GDBRemoteCommunication::PacketResult
+GDBRemoteCommunication::ReadPacketWithOutputSupport(
+    StringExtractorGDBRemote &response, Timeout<std::micro> timeout,
+    bool sync_on_timeout,
+    llvm::function_ref<void(llvm::StringRef)> output_callback) {
+  auto result = ReadPacket(response, timeout, sync_on_timeout);
+  while (result == PacketResult::Success && response.IsNormalResponse() &&
+         response.PeekChar() == 'O') {
+    response.GetChar();
+    std::string output;
+    if (response.GetHexByteString(output))
+      output_callback(output);
+    result = ReadPacket(response, timeout, sync_on_timeout);
+  }
+  return result;
+}
+
+GDBRemoteCommunication::PacketResult
 GDBRemoteCommunication::ReadPacket(StringExtractorGDBRemote &response,
                                    Timeout<std::micro> timeout,
                                    bool sync_on_timeout) {