default or selected kernelversion does not have config value CONFIG_RTC_MC146818_LIB.
Result is shown for kernelversion 6.9-rc1

CONFIG_RTC_MC146818_LIB (not configurable)

modulename: rtc-mc146818-lib.ko

configname: CONFIG_RTC_MC146818_LIB

Linux Kernel Configuration
└─>Device Drivers
└─>RTC_MC146818_LIB
In linux kernel since version 4.1 (release Date: 2015-06-21)  
source code: