CONFIG_MIPS_MAGNUM_4000 is not available for thedefaultarchitecture x86.
Result is shown for architecture mips

Support for MIPS Magnum 4000

configname: CONFIG_MIPS_MAGNUM_4000

Linux Kernel Configuration
└─>Support for MIPS Magnum 4000
In linux kernel since version 2.6.12  
This is a machine with a R4000 100 MHz CPU. To compile a Linux
kernel that runs on these, say Y here. For details about Linux on
the MIPS architecture, check out the Linux/MIPS FAQ on the WWW at
<http://www.linux-mips.org/>.