看清楚！！！！！！！！！！！！
This method, while much slower, will rebuild your whole system to ensure that
everything has been rebuilt with your new compiler, and therefore safer. At
first, you will upgrade GCC and libtool and switch to your new compiler.
这句话之前已经够了。这句话只是说如果你希望吧新系统用新的gcc编译一边，就执行一下。毫无必要的
