CONFIG_MIPS32_N32 is not available for thedefaultarchitecture x86.
Result is shown for architecture 64BIT or mips

Kernel support for n32 binaries

modulename: binfmt_elfn32.ko

configname: CONFIG_MIPS32_N32

Linux Kernel Configuration
└─>Kernel support for n32 binaries
In linux kernel since version 2.6.12  
Select this option if you want to run n32 binaries. These are
64-bit binaries using 32-bit quantities for addressing and certain
data that would normally be 64-bit. They are used in special
cases.

If unsure, say N.

source code: