CONFIG_ARC_DBG is not available for thedefaultarchitecture x86.
Result is shown for architecture arc

ARC debugging

configname: CONFIG_ARC_DBG

Linux Kernel Configuration
└─>ARC Architecture Configuration
└─>ARC debugging
In linux kernel since version 3.1 (release Date: 2011-10-24)  
is selected by
CONFIG_ARC_DW2_UNWIND