CONFIG_SUN3 is not available for thedefaultarchitecture x86.
Result is shown for architecture m68k

Sun3 machine support

modulename: config.ko

and/or

sun3-head.ko

configname: CONFIG_SUN3

CPU/machine family support
└─>Sun3 machine support
In linux kernel since version 2.6.12  
This option enables support for the Sun 3 series of workstations
(3/50, 3/60, 3/1xx, 3/2xx systems). These use a classic 68020 CPU
but the custom memory management unit makes them incompatible with
all other classic m68k machines, including Sun 3x.

source code:
selects
CONFIG_HAVE_ARCH_PFN_VALID
CONFIG_LEGACY_TIMER_TICK
CONFIG_NO_DMA
CONFIG_M68020

depends
CONFIG_MMU

is selected by
CONFIG_SUN3_SCSI