EPA: Keep location for FunBind GRHSs
When making a FunBind, in PostProcess, we discard the location for the grhss
checkFunBind strictness locF ann (L lf fun) is_infix pats (L _ grhss)
But if we keep it, it marks the anchor for the =, meaning we can freely update the pats without worrying about spacing from the pats to the =.