还原spawn (#18)

* 还原spawn

* 还原spawn逻辑

src/std/sys/unix/process/process_unix.rs

@@ -157,8 +157,6 @@ impl Command {
             let mut p = unsafe { Process::new(pid, pidfd) };
             let mut bytes = [0; 8];
 
-            //TODO: 这里直接返回，没有从管道读取子进程状态，后续需更改
-            return Ok((p, ours));
             // loop to handle EINTR
             loop {
                 match input.read(&mut bytes) {