CONFIG_MIPS32_COMPAT is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_MIPS32_COMPAT (not configurable)

modulename: linux32.ko

configname: CONFIG_MIPS32_COMPAT

Linux Kernel Configuration
└─>MIPS32_COMPAT
In linux kernel since version 2.6.12  
source code:
arch/mips/kernel/