CONFIG_EXPOLINE_EXTERN is not available for thedefaultarchitecture x86.
Result is shown for architecture s390

CONFIG_EXPOLINE_EXTERN (not configurable)

modulename: expoline.ko

configname: CONFIG_EXPOLINE_EXTERN

Linux Kernel Configuration
└─>Processor type and features
└─>EXPOLINE_EXTERN
In linux kernel since version 4.14.326 (release Date: 2023-09-23)  
Generate expolines as external functions if the compiler supports it.
This option is required for some tooling like kpatch, if expolines
are enabled. The kernel is compiled with
-mindirect-branch=thunk-extern, which requires a newer compiler.

source code: