CONFIG_CLOCK_SET is not available for thedefaultarchitecture x86.
Result is shown for architecture m68k
default or selected kernelversion does not have config value CONFIG_CLOCK_SET.
Result is shown for kernelversion 6.5.1

Enable setting the CPU clock frequency

configname: CONFIG_CLOCK_SET

Linux Kernel Configuration
└─>Enable setting the CPU clock frequency
In linux kernel since version 2.6.18 (release Date: 2006-09-19)  
On some CPU's you do not need to know what the core CPU clock
frequency is. On these you can disable clock setting. On some
traditional 68K parts, and on all ColdFire parts you need to set
the appropriate CPU clock frequency. On these devices many of the
onboard peripherals derive their timing from the master CPU clock