CONFIG_SIBYTE_HAS_LDT is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_SIBYTE_HAS_LDT (not configurable)

configname: CONFIG_SIBYTE_HAS_LDT

Linux/MIPS Kernel Configuration
└─>Machine selection
└─>SIBYTE_HAS_LDT
In linux kernel since version 2.6.12