CONFIG_XTENSA_PLATFORM_ISS is not available for thedefaultarchitecture x86.
Result is shown for architecture xtensa

ISS

configname: CONFIG_XTENSA_PLATFORM_ISS

Xtensa System Type
└─>ISS
In linux kernel since version 2.6.13 (release Date: 2005-08-28)  
ISS is an acronym for Tensilica's Instruction Set Simulator.