CONFIG_NIOS2_HW_MUL_SUPPORT is not available for thedefaultarchitecture x86.
Result is shown for architecture nios2

Enable MUL instruction


Linux Kernel Configuration
└─>Platform options
└─>Enable MUL instruction
In linux kernel since version 3.19 (release Date: 2015-02-08)  
Set to true if you configured the Nios II to include the MUL
instruction. This will enable the -mhw-mul compiler flag.