CONFIG_460SX is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

CONFIG_460SX (not configurable)

configname: CONFIG_460SX

Linux Kernel Configuration
└─>460SX
In linux kernel since version 2.6.30 (release Date: 2009-06-09)  

is depended by
CONFIG_REDWOOD
CONFIG_EIGER