CONFIG_SPARC_LEON is not available for thedefaultarchitecture x86.
Result is shown for architecture sparc

Sparc Leon processor family

modulename: leon_kernel.ko

and/or

leon_mm.ko

and/or

setup-bus.ko

and/or

setup-irq.ko

configname: CONFIG_SPARC_LEON

Linux/SPARC Kernel Configuration
└─>Processor type and features
└─>Sparc Leon processor family
In linux kernel since version 2.6.32 (release Date: 2009-12-02)  
If you say Y here if you are running on a SPARC-LEON processor.
The LEON processor is a synthesizable VHDL model of the
SPARC-v8 standard. LEON is part of the GRLIB collection of
IP cores that are distributed under GPL. GRLIB can be downloaded
from www.gaisler.com. You can download a sparc-linux cross-compilation
toolchain at www.gaisler.com.

source code: