Ref: http://forums.funtoo.org/topic/938-missing-devrtc-in-genkernel-of-gentoo-sources-446/

I ran
emerge gentoo-sources
genkernel all
and the kernel which got built did not include /dev/rtc. This resulted in clock problems on my system. Should this driver be included by default?

I was able to correct this by running genkernel --menuconfig all and enabling Device Drivers / Real time Clock.