读取当前的.config文件，然后向用户弹出这些配置选项中的但是没有在.config中的选项给用户选择。当用户将配置移植到新的内核时，很有用。
It reads the existing
.configfile and prompts the user for options in the current kernel source that are not found in the file. This is useful when taking an existing configuration and moving it to a new kernel.
Refs