CONFIG_CPU_LOONGSON3 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips
default or selected kernelversion does not have config value CONFIG_CPU_LOONGSON3.
Result is shown for kernelversion 6.8.2

Loongson 3 CPU

configname: CONFIG_CPU_LOONGSON3

CPU type
└─>Loongson 3 CPU
In linux kernel since version 3.10 (release Date: 2013-06-30)  
The Loongson 3 processor implements the MIPS64R2 instruction
set with many extensions.