CONFIG_CPU_THUMBONLY is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
CONFIG_CPU_THUMBONLY (not configurable)
configname: CONFIG_CPU_THUMBONLY
Linux Kernel Configuration
└─>CPU_THUMBONLY
In linux kernel since version 3.1 (release Date: 2011-10-24)
Select this if your CPU doesn't support the 32 bit ARM instructions.