gdbstub: Set current CPU on interruptions

gdb expects that the thread ID for c and g-class operations is set to
the CPU we provide when reporting VM stop conditions. If the stub is
still tuned to a different CPU, the wrong information is delivered to
the gdb frontend.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

gdbstub.c

@@ -1285,6 +1285,7 @@ static void gdb_vm_state_change(void *opaque, int running, RunState state)
         ret = GDB_SIGNAL_UNKNOWN;
         break;
     }
+    gdb_set_stop_cpu(cpu);
     snprintf(buf, sizeof(buf), "T%02xthread:%02x;", ret, cpu_index(cpu));
 
 send_packet: