This commit implements stderr redirection in HSN, support
Bash-like syntax for redirecting standard error output.
Support both foreground and background commands.
example:
- nsh> ls noexists 2> err.log
- nsh> ls noexists 2> err.log &
- nsh> ls noexists 2>> err.log
- nsh> sh < /dev/ttyS0 > /dev/ttyS0 2> /dev/ttyS1 &
- nsh> sh < /dev/ttyS0 > /dev/ttyS0 2>&1 &
Signed-off-by: fangpeina <fangpeina@xiaomi.com>
78420bc022