CONFIG_NR_IRQS is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

Number of virtual interrupt numbers

configname: CONFIG_NR_IRQS

Linux Kernel Configuration
└─>Number of virtual interrupt numbers
In linux kernel since version 2.6.33 (release Date: 2010-02-24)  
This defines the number of virtual interrupt numbers the kernel
can manage. Virtual interrupt numbers are what you see in
/proc/interrupts. If you configure your system to have too few,
drivers will fail to load or worse - handle with care.