CONFIG_MACH_LOONGSON is not available for thedefaultarchitecture x86.
Result is shown for architecture mips
default or selected kernelversion does not have config value CONFIG_MACH_LOONGSON.
Result is shown for kernelversion 6.5.1

Loongson family of machines

configname: CONFIG_MACH_LOONGSON

System type
└─>Loongson family of machines
In linux kernel since version 2.6.32 (release Date: 2009-12-02)  
This enables the support of Loongson family of machines.

Loongson is a family of general-purpose MIPS-compatible CPUs.
developed at Institute of Computing Technology (ICT),
Chinese Academy of Sciences (CAS) in the People's Republic
of China. The chief architect is Professor Weiwu Hu.