CONFIG_CPU_SUBTYPE_SHX3 is not available for thedefaultarchitecture x86.
Result is shown for architecture sh

Support SH-X3 processor

modulename: setup-shx3.ko

configname: CONFIG_CPU_SUBTYPE_SHX3

Processor sub-type selection
└─>Support SH-X3 processor
In linux kernel since version 2.6.23 (release Date: 2007-10-09)  
source code:
arch/sh/kernel/cpu/sh4a/setup-shx3.c