CONFIG_KEXEC is not available for the selected architecture x86.
Result is shown for architecture s390

CONFIG_KEXEC (not configurable)

modulename: machine_kexec.ko

and/or

kexec.ko

configname: CONFIG_KEXEC

Linux Kernel Configuration
└─>Processor type and features
└─>KEXEC
In linux kernel since version 2.6.13 (release Date: 2005-08-28)
source code:
arch/mips/kernel/