CONFIG_MACH_TXX9 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_MACH_TXX9 (not configurable)

configname: CONFIG_MACH_TXX9

Linux Kernel Configuration
└─>MACH_TXX9
In linux kernel since version 2.6.27 (release Date: 2008-10-09)  

is selected by
CONFIG_TOSHIBA_FPCIB0