gdbstub: replace exit calls with proper shutdown for softmmu

This replaces the exit calls by shutdown requests, ensuring a proper
cleanup of Qemu. Features like net/vhost-vdpa.c are expecting
qemu_cleanup to be called to remove their last residuals.

Signed-off-by: Clément Chigot <chigot@adacore.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20231003071427.188697-6-chigot@adacore.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

gdbstub/system.c

@@ -435,6 +435,12 @@ void gdb_exit(int code)
     qemu_chr_fe_deinit(&gdbserver_system_state.chr, true);
 }
 
+void gdb_qemu_exit(int code)
+{
+    qemu_system_shutdown_request_with_code(SHUTDOWN_CAUSE_GUEST_SHUTDOWN,
+                                           code);
+}
+
 /*
  * Memory access
  */