update libcpu/arm/cortex-m4: support lazy stack optimized.
update scons script: support THUMB-2 CODE.
Update SConscript
Update rtthread-lpc17xx.ld
Update SConscript
Merge pull request #112 from aozima/pulls

update libcpu/arm/cortex-m4: support lazy stack optimized.
Add rt_kprintf re-defined, which is suggested by ufbycd.
Update kservice.c