CONFIG_PPC_CLOCK is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

CONFIG_PPC_CLOCK (not configurable)

modulename: clock.ko

configname: CONFIG_PPC_CLOCK

Linux/PowerPC Kernel Configuration
└─>PPC_CLOCK
In linux kernel since version 2.6.24 (release Date: 2008-01-24)  
source code:
arch/powerpc/kernel/clock.c
selects
CONFIG_HAVE_CLK

is depended by
CONFIG_PPC_MPC512x