参照：http://docs.widora.io/zh/uboot编译
Assembler messages:
Error: unknown architecture `4kc'
Error: unrecognized option -march=4kc
cc1: error: unrecognized command line option '-mabicalls'
cc1: error: bad value (4kc) for -march switch
cc1: error: bad value (4kc) for -mtune switch
make: *** [cpu/ralink_soc/start.o] Error 2