Improve handling of multiple successive continue packets in non-stop
mode. More specifically:
- Explicitly send error response (instead of crashing on assertion) if the user attempts to resume the same process twice. Since we do not support thread-level non-stop mode, one needs to always stop the process explicitly before resuming another thread set.
- Actually stop the process if "vCont;t" is delivered to a running process. Similarly, we only support stopping all the running threads simultaneously and return an error if the action would result in a subset of threads still running.
With this patch, running multiple processes simultaneously is still
unsupported. The patch also employs a hack to avoid enabling stdio
forwarding on "vCont;t" packet. Both of these issues will be addressed
by followup patches.
Sponsored by: The FreeBSD Foundation