!372 [本次提交内容：在TI公司C6000 DSP处理器上成功移植rt-thread操作系统；主要在libcpu/ti-dsp/c6x添加keystone架构底层代码，在bsp/ti-c6678添加bsp工程，该工程已在本人的开发板上成功运行]
Merge pull request !372 from hdwei/hdwei

添加READM.md说明文档

[update] RT-Thread Robot automatic submission

* [cpu] 增加ARCH_CPU_BIG_ENDIAN
- 之前RT_USING_BIG_ENDIAN的命名并不合理，予以替换为ARCH_CPU_BIG_ENDIAN
- 删除一处多余的ARCH_CPU_64BIT
- 整理了libcpu/Kconfig的格式

* [libcpu][Kconfig] Cortex-M4&7 select ARCH_ARM_CORTEX_FPU

* revert last commit

* 1.修改template.uvproj文件所伴随的改动
* 1.编译选项指定C99格式，解决编译错误declaration may not appear after executable statem…
* 1.修复找不到函数rt_interrupt_dispatch错误

tcpclient.c udpserver.c and udpclient.c
Formatting
Co-authored-by: Man, Jianting (Meco) <920369182@qq.com>

* [posix][io]整理posix/io文件夹
- 将select.c移入到poll文件夹
- 将libc.c移入到tty文件夹，isatty函数归并到libc.c中, termios并入tty文件夹中
- 整理Sconscript
Signed-off-by: Meco Man <920369182@qq.com>

* [libc][newlib]调整文件夹结构

* 避免警告，变量可能未初始化就使用

* 避免警告，变量可能未初始化就使用

* 避免警告，变化可能未初始化就使用。

* Update bsp/stm32/libraries/HAL_Drivers/drv_usart.c
Co-authored-by: Nguo <guozhanxin@rt-thread.com>

* Update bsp/stm32/libraries/HAL_Drivers/drv_usart_v2.c
Co-authored-by: Nguo <guozhanxin@rt-thread.com>
Co-authored-by: Nguo <guozhanxin@rt-thread.com>

[sconscript.platform] 优化针对编译器判断

- 移除2.0.2，该版本存在几个重要的bug，已经在2.0.3中修复，作者强烈建议更新
- 将部分bsp由2.0.2调整为2.0.3

* [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.

[kernel][pm] beautify code

[update] change ccflags to cflags

- 删除啰嗦的代码
related: https://github.com/RT-Thread/rt-thread/issues/3046