RT-Thread/rt-thread: KM https://github.com/RT-Thread/rt-thread.git @ 28e8e6da62f878f3baa6fbddc4dcdb8744497bf7

Meco Man fa8e8ed31f add RTM_EXPORT label for unistd.c		5 lat temu
..
sys	291fe36139 [pthread][libc] move 'clock_time' to libc	5 lat temu
SConscript	b3ab8a99e1 Signed-off-by: mysterywolf	5 lat temu
readme.md	d5f8830177 add newlib/dlib readme	5 lat temu
termios.h	54143409ca 增加#include <rtconfig.h> 防止开启termios功能后报错	5 lat temu
time.c	417f8b9bed update	5 lat temu
unistd.c	fa8e8ed31f add RTM_EXPORT label for unistd.c	5 lat temu

Attentions

This folder is "common" for armlibc newlibc and dlib. It's not "common" for minilibc.
If you want to add new .c files, please do not forget to fix SConscript file too. eg:
```
if GetDepend('RT_USING_POSIX') == False:
    SrcRemove(src, ['unistd.c'])
```