CONFIG_SYS_HAS_CPU_TX49XX is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

CONFIG_SYS_HAS_CPU_TX49XX (not configurable)

configname: CONFIG_SYS_HAS_CPU_TX49XX

Linux/MIPS Kernel Configuration
└─>CPU selection
└─>SYS_HAS_CPU_TX49XX
In linux kernel since version 2.6.15 (release Date: 2006-01-02)  
is selected by
CONFIG_CPU_TX49XX

is depended by
CONFIG_TOSHIBA_RBTX4927