Clang ThinLTO (EXPERIMENTAL)

configname: CONFIG_LTO_CLANG_THIN

Link Time Optimization (LTO)
└─>Clang ThinLTO (EXPERIMENTAL)
In linux kernel since version 5.2 (release Date: 2019-07-07)  
This option enables Clang's ThinLTO, which allows for parallel
optimization and faster incremental compiles compared to the
CONFIG_LTO_CLANG_FULL option. More information can be found
from Clang's documentation:

https://clang.llvm.org/docs/ThinLTO.html

If unsure, say Y.