[libc][armlibc] Fix getchar error after exit vi
[libc][armlibc] Fix getchar error after exit vi

 - _sys_istty() add stdio as tty
 - without this, after exit vi program getchar will return -1, I don't know why it works

hezlog/rt-thread,weiyuliang/rt-thread,geniusgogo/rt-thread,geniusgogo/rt-thread,FlyLu/rt-thread,gbcwbz/rt-thread,nongxiaoming/rt-thread,zhaojuntao/rt-thread,gbcwbz/rt-thread,weiyuliang/rt-thread,armink/rt-thread,gbcwbz/rt-thread,AubrCool/rt-thread,weiyuliang/rt-thread,zhaojuntao/rt-thread,RT-Thread/rt-thread,hezlog/rt-thread,armink/rt-thread,wolfgangz2013/rt-thread,weety/rt-thread,nongxiaoming/rt-thread,RT-Thread/rt-thread,ArdaFu/rt-thread,armink/rt-thread,weiyuliang/rt-thread,weiyuliang/rt-thread,armink/rt-thread,geniusgogo/rt-thread,AubrCool/rt-thread,ArdaFu/rt-thread,FlyLu/rt-thread,weety/rt-thread,FlyLu/rt-thread,wolfgangz2013/rt-thread,AubrCool/rt-thread,gbcwbz/rt-thread,armink/rt-thread,wolfgangz2013/rt-thread,hezlog/rt-thread,armink/rt-thread,zhaojuntao/rt-thread,RT-Thread/rt-thread,wolfgangz2013/rt-thread,RT-Thread/rt-thread,AubrCool/rt-thread,ArdaFu/rt-thread,weety/rt-thread,weety/rt-thread,geniusgogo/rt-thread,ArdaFu/rt-thread,gbcwbz/rt-thread,AubrCool/rt-thread,gbcwbz/rt-thread,geniusgogo/rt-thread,FlyLu/rt-thread,RT-Thread/rt-thread,armink/rt-thread,FlyLu/rt-thread,wolfgangz2013/rt-thread,RT-Thread/rt-thread,ArdaFu/rt-thread,weety/rt-thread,wolfgangz2013/rt-thread,FlyLu/rt-thread,weety/rt-thread,hezlog/rt-thread,zhaojuntao/rt-thread,nongxiaoming/rt-thread,nongxiaoming/rt-thread,zhaojuntao/rt-thread,RT-Thread/rt-thread,hezlog/rt-thread,geniusgogo/rt-thread,geniusgogo/rt-thread,nongxiaoming/rt-thread,gbcwbz/rt-thread,wolfgangz2013/rt-thread,weiyuliang/rt-thread,ArdaFu/rt-thread,AubrCool/rt-thread,weiyuliang/rt-thread,FlyLu/rt-thread,hezlog/rt-thread,zhaojuntao/rt-thread,weety/rt-thread,hezlog/rt-thread,AubrCool/rt-thread,ArdaFu/rt-thread,zhaojuntao/rt-thread,nongxiaoming/rt-thread,nongxiaoming/rt-thread