CONFIG_ARCH_GUMSTIX is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Gumstix XScale boards

modulename: gumstix.ko

configname: CONFIG_ARCH_GUMSTIX

Select target board
└─>Gumstix XScale boards
In linux kernel since version 2.6.26 (release Date: 2008-07-13)  
Say Y here if you intend to run this kernel on a
Gumstix Full Function Minature Computer.

source code:
arch/arm/mach-pxa/gumstix.c
selects

CONFIG_PXA25x


is selected by
CONFIG_MACH_GUMSTIX_F