[BSP] fix GCC compiling issue in LPC408x bsp

romfs: declare the dummy entry as weak

[Sensor] code cleanup

[C++] fix GCC compiling issue. 

Add cplusplus and sensor framework.

[LIBC] Use RT_USING_LIBC instead of libs option for each compiler

finsh: allow user to disable the FINSH_USING_HISTORY

Add mb9bf568r to bsp

Misc fix

Use signed int as array index is unsecure.

tools: fix SrcRemove on empty src

If the src is empty list, it will crash at:

    IndexError: list index out of range:
      File "/home/xxx/src/SConstruct", line 39:
        objs = PrepareBuilding(env, RTT_ROOT, has_libcpu=True)
      ...
      File "/home/xxx/src/drivers/SConscript", line 12:
        SrcRemove(src, src_need_remove)
      File "/home/rt-thread-stable/tools/building.py", line 496:
        if type(src[0]) == type('str'):