CONFIG_MIPS32_O32 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

Kernel support for o32 binaries

modulename: binfmt_elfo32.ko

configname: CONFIG_MIPS32_O32

Linux Kernel Configuration
└─>Executable file formats
└─>Kernel support for o32 binaries
In linux kernel since version 2.6.12  
Select this option if you want to run o32 binaries. These are pure
32-bit binaries as used by the 32-bit Linux/MIPS port. Most of
existing binaries are in this format.

If unsure, say Y.

source code: