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

Sun3 support

modulename: config.ko

configname: CONFIG_SUN3

Linux Kernel Configuration
└─>Sun3 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). Enabling this option requires
that all other hardware types must be disabled, as Sun 3 kernels
are incompatible with all other m68k targets (including Sun 3x!).

If you don't want to compile a kernel exclusively for a Sun 3, say N.

source code: