CONFIG_IA64 is not available for thedefaultarchitecture x86.
Result is shown for architecture ia64

CONFIG_IA64 (not configurable)

configname: CONFIG_IA64

Linux Kernel Configuration
└─>Processor type and features
└─>IA64
In linux kernel since version 2.6.12  
The Itanium Processor Family is Intel's 64-bit successor to
the 32-bit X86 line. The IA-64 Linux project has a home
page at <http://www.linuxia64.org/> and a mailing list at
<linux-ia64@vger.kernel.org>.


is selected by
CONFIG_MSPEC