Option to fail Xilinx process if pins are unconstrained
I've never found that option - much as I'd love to have it! The closest I've found is the opposite: "fail if there are things constrained which don't exist".

My (Windows CMD.exe) workaround is a post-map script which looks in the .pad file for the string "|UNLOCATED|".  

@find "|UNLOCATED|" %DESIGN%.pad || goto padsok