compiler made by RSB

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I'm new here,and followed the guide to make my own compiler by RSB。
is this tool made the best suitable compiler ?  I'm not expert on this but 
tools like crosstool-ng can configure detailly , for example if you config 
a ARM cpu you choose armv6/armv7 , soft/hard float point unit etc。
precise configuration makes compiler generates  effective machine code?  
in RSB I see only one config file for ARM。how does it adapt to all architecture
variants ？