CONFIG_THUMB2_KERNEL is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Compile the kernel in Thumb-2 mode (EXPERIMENTAL)

configname: CONFIG_THUMB2_KERNEL

Linux Kernel Configuration
└─>Kernel Features
└─>Compile the kernel in Thumb-2 mode (EXPERIMENTAL)
In linux kernel since version 2.6.32 (release Date: 2009-12-02)  
By enabling this option, the kernel will be compiled in
Thumb-2 mode. A compiler/assembler that understand the unified
ARM-Thumb syntax is needed.

If unsure, say N.