CONFIG_MACH_TX49XX is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

Toshiba TX49 series based machines

configname: CONFIG_MACH_TX49XX

System type
└─>Toshiba TX49 series based machines
In linux kernel since version 2.6.27 (release Date: 2008-10-09)  

is selected by
CONFIG_NE2000