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