Poll failure just means poll failed. It's safer to assume the target is
still running, because then if it is running and subsequently halts we can
relay this to gdb correctly. We can't do the other way around, because once
gdb thinks the target has halted, it can't deal with it spontaneously
running.
Change-Id: Idb56137f1d6baa9afc1b0e55e4a48f407b8ebe83
Signed-off-by: Tim Newsome <tim@sifive.com>