CONFIG_RISCV_ALTERNATIVE is not available for thedefaultarchitecture x86.
Result is shown for architecture riscv

CONFIG_RISCV_ALTERNATIVE (not configurable)

modulename: alternative.ko

configname: CONFIG_RISCV_ALTERNATIVE

Linux Kernel Configuration
└─>Platform type
└─>RISCV_ALTERNATIVE
In linux kernel since version 4.14.326 (release Date: 2023-09-23)  
This Kconfig allows the kernel to automatically patch the
errata required by the execution platform at run time. The
code patching is performed once in the boot stages. It means
that the overhead from this mechanism is just taken once.

source code:
depends
NOT CONFIG_XIP_KERNEL

is selected by
CONFIG_RISCV_ISA_SVPBMT

is depended by
CONFIG_RISCV_ISA_SVPBMT