Merge pull request #1 from RT-Thread/master

sync
[GDB stub]first version
[bsp]add gdb support for stm32f4xx
[libcpu]am335x edit vector

vector_undef and vector_dabt
[bsp]add gdb support for BBB
Revert "[bsp]add gdb support for BBB"

This reverts commit a966dd3c3802198cf84adbd8aef08d9206e256ce.
[bsp]add gdb support for BBB
[bsp]stm32f4xx typo
拼写错误

drvers->drivers
[shell] Fix compiling issue when DFS is not enable
[Kernel] comments clean up.
[libcpu] Add builtin ffs implementation for Cortex-M4.
[Kernel] comments clean up.
[LogTrace] Use OFLAG_RDWR to replace FLAG_RDWR when opening a device.
[Kernel] Use stream mode to open console device.
Merge branch 'master' of https://github.com/RT-Thread/rt-thread
Merge pull request #339 from tcz717/patch-1

[bsp] Fix the spelling errors.
[Ymodem]When active end the session, It can config send CAN number.
[Ymodem]Add device open flag as input parameter to ymodem function.
[BSP]Fixes two writing mistake for stm32f10x.