CONFIG_ARC_HAS_PAE40 is not available for thedefaultarchitecture x86.
Result is shown for architecture arc

Support for the 40-bit Physical Address Extension

configname: CONFIG_ARC_HAS_PAE40

Linux Kernel Configuration
└─>ARC Architecture Configuration
└─>Support for the 40-bit Physical Address Extension
In linux kernel since version 4.1 (release Date: 2015-06-21)  
Enable access to physical memory beyond 4G, only supported on
ARC cores with 40 bit Physical Addressing support