CONFIG_SLS is not available for thedefaultarchitecture x86.
Result is shown for architecture 64BIT

Mitigate Straight-Line-Speculation

configname: CONFIG_SLS

Linux Kernel Configuration
└─>Mitigations for CPU vulnerabilities
└─>Mitigate Straight-Line-Speculation
In linux kernel since version 4.14.326 (release Date: 2023-09-23)  
Compile the kernel with straight-line-speculation options to guard
against straight line speculation. The kernel image might be slightly
larger.

selects
CONFIG_OBJTOOL