CONFIG_SYS_SUPPORTS_64BIT_KERNEL is not available for thedefaultarchitecture x86.
Result is shown for architecture mips
CONFIG_SYS_SUPPORTS_64BIT_KERNEL (not configurable)
configname: CONFIG_SYS_SUPPORTS_64BIT_KERNEL
Linux/MIPS Kernel Configuration
└─>SYS_SUPPORTS_64BIT_KERNEL