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

CONFIG_CPU_SPECTRE (not configurable)

configname: CONFIG_CPU_SPECTRE

Linux Kernel Configuration
└─>CPU_SPECTRE
In linux kernel since version 4.2 (release Date: 2015-08-30)  
is depended by
CONFIG_CPU_V7