* Synchronize the code of the rt mart branch to the master branch.
  * TTY device
  * Add lwP code from rt-smart
  * Add vnode in DFS, but DFS will be re-write for rt-smart
  * There are three libcpu for rt-smart:
    * arm/cortex-a, arm/aarch64
    * riscv64
Co-authored-by: NRbb666 <zhangbingru@rt-thread.com>
Co-authored-by: Nzhkag <zhkag@foxmail.com>

目前基本功能已经可以在QEMU上跑起来，但是pthread和内核signal选中会报冲突。先合并一版本，后续解决这些问题。

* implement extension standard C functions

* [add] the function realization of signal for posix.
* [update] the posix support for armclang.
* [add] the new macro "RT_USING_POSIX_TIMER".
* [modify] select "RT_USING_SOFT_TIMER" when use posix'timer.
* [bug] optimize the logic for the "time_xxx" functions.
* [modify] use "RT_USING_POSIX_TIMER" to protect the macro definition.
* [modify] error code when except happened.
* [delete] the "environ" is useless at this time.

Update license for RT-Thread kernel.

Add cconfig.h file for different version of GCC, which is automatically
detected and generated by scons script.

1. Remove components.h file;
2. Add libc_* files for standard libc definitions;
3. Add rtdbg.h file for simple debug log;
4. Add single list implementation;
5. Change the 'rt_uint8_t' type of cmd to 'int'.