CONFIG_MMU_SUN3 is not available for thedefaultarchitecture x86.
Result is shown for architecture m68k

CONFIG_MMU_SUN3 (not configurable)

modulename: sun3kmap.ko

configname: CONFIG_MMU_SUN3

Linux/68k Kernel Configuration
└─>Platform dependent setup
└─>MMU_SUN3
In linux kernel since version 2.6.12  
source code:
arch/m68k/mm/
is selected by
CONFIG_SUN3X