CONFIG_CPU_S3C6400_CLOCK is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_CPU_S3C6400_CLOCK (not configurable)

modulename: s3c6400-clock.ko

configname: CONFIG_CPU_S3C6400_CLOCK

Linux Kernel Configuration
└─>CPU_S3C6400_CLOCK
In linux kernel since version 2.6.29 (release Date: 2009-03-23)  
Common clock support code for the S3C6400 that is shared
by other CPUs in the series, such as the S3C6410.

source code:
arch/arm/plat-s3c64xx/s3c6400-clock.c