[sleep] 加入调度器尚未运行时的延时情况

[libc][rtlibc] remove libc_ioctl.h

[update] usleep supports calling in interrupts.

Update drv_rtc.c

[kernel] 补充endif后缀注释

[master][rtlibc] remove libc_errno.h & libc_limits.h

[bsp][zynqmp-r5-axu4ev]修复使用xil_cache.h可能找不到函数定义的问题

update board.c in k210 bsp

[example] 解决潜在内存问题

不需要再判断是否开启libc

重新解决冲突，源自：https://gitee.com/rtthread/rt-thread/pulls/48/files

[src] add RT_WEAK for rt_malloc_align,rt_free_align

/bsp/k210:add delay us function in board.c ,when using posix interface ,rt_hw_us_delay this function will be called in unistd.c file

将rt_int32_t改为time_t。

[bsp][gd32450] Fix the wrong judgment with CAN_STAT_IWS flag

Merge pull request !217 from cyz/cyz

[tools] Optimization the EXTERN_LIB variable use

[tools] update eclipse project after dist.

[msh] implement tail command

[kernel]补充endif后缀注释