Change Details

Complete libxo transition. I remove `atexit` because we need call xo_finish manually for checking the return value of xo_finish.

Complete libxo transition. I remove `atexit` because we need call `xo_finish` manually for checking the return value of xo_finish. To achive POSIX standard (print an error message to `stderr` and return a non-zero exit code if they fail to write to `stdout`).

Complete libxo transition. I remove `atexit` because we need call `xo_finish` manually for checking the return value of xo_finish. To achive POSIX standard (print an error message to `stderr` and return a non-zero exit code if they fail to write to `stdout`).