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

CONFIG_CPU_THUMB_CAPABLE (not configurable)

configname: CONFIG_CPU_THUMB_CAPABLE

Linux Kernel Configuration
└─>CPU_THUMB_CAPABLE
In linux kernel since version 4.2 (release Date: 2015-08-30)  
Select this if your CPU can support Thumb mode.