CONFIG_SPARC64 is not available for thedefaultarchitecture x86.
Result is shown for architecture sparc64

CONFIG_SPARC64 (not configurable)

configname: CONFIG_SPARC64

Linux Kernel Configuration for 64-bit SPARC
└─>SPARC64
In linux kernel since version 2.6.12  

is selected by
CONFIG_LEDS_SUNFIRE