[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

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

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

[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

[bug][kernel][heap] 将内存堆信号量保护机制由FIFO改为PRIO

revert #3647

[tools] remove formatting

fixed bug of lcd_draw_line function when y1 == y2. need to consider u…

[kernel] 对rt_tick变量增加volatile修饰，防止编译器优化时出现问题

[bug][kernel] 保持空闲任务钩子函数调用的原子性

[src][memheap]Fix the crash problem after opening Oz optimization on ac6.

update Arm ToolChains to 10-2020-q4.