qemu-char: using qemu_set_nonblock() instead of fcntl(O_NONBLOCK)

Technically, fcntl(soc, F_SETFL, O_NONBLOCK)
is incorrect since it clobbers all other file flags.
We can use F_GETFL to get the current flags, set or
clear the O_NONBLOCK flag, then use F_SETFL to set the flags.

Using the qemu_set_nonblock() wrapper.
Signed-off-by: NWangxin <wangxinxin.wang@huawei.com>
Signed-off-by: NGonglei <arei.gonglei@huawei.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

qemu-char.c

@@ -975,7 +975,7 @@ static CharDriverState *qemu_chr_open_fd(int fd_in, int fd_out)
     s = g_malloc0(sizeof(FDCharDriver));
     s->fd_in = io_channel_from_fd(fd_in);
     s->fd_out = io_channel_from_fd(fd_out);
-    fcntl(fd_out, F_SETFL, O_NONBLOCK);
+    qemu_set_nonblock(fd_out);
     s->chr = chr;
     chr->opaque = s;
     chr->chr_add_watch = fd_chr_add_watch;
@@ -1062,7 +1062,7 @@ static CharDriverState *qemu_chr_open_stdio(ChardevStdio *opts)
     }
     old_fd0_flags = fcntl(0, F_GETFL);
     tcgetattr (0, &oldtty);
-    fcntl(0, F_SETFL, O_NONBLOCK);
+    qemu_set_nonblock(0);
     atexit(term_exit);
 
     chr = qemu_chr_open_fd(0, 1);