CONFIG_SYNC_R4K is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_SYNC_R4K (not configurable)

modulename: sync-r4k.ko

configname: CONFIG_SYNC_R4K

Linux Kernel Configuration
└─>SYNC_R4K
In linux kernel since version 2.6.26 (release Date: 2008-07-13)  
source code:
arch/mips/kernel/sync-r4k.c
is depended by
CONFIG_MIPS_CMP