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

Gumstix XScale 255 boards

modulename: gumstix.ko

configname: CONFIG_ARCH_GUMSTIX

Linux Kernel Configuration
└─>Intel PXA2xx/PXA3xx Implementations
└─>Gumstix XScale 255 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
Basix, Connex, ws-200ax, ws-400ax systems

source code:
selects
CONFIG_PXA25x

depends
CONFIG_ARCH_PXA