CONFIG_TUNE_Z990 is not available for thedefaultarchitecture x86.
Result is shown for architecture s390

IBM zSeries model z890 and z990

configname: CONFIG_TUNE_Z990

Tune code generation
└─>IBM zSeries model z890 and z990
In linux kernel since version 3.10 (release Date: 2013-06-30)  
depends
NOT CONFIG_CC_IS_CLANG