In File::Stat::Bits these (and some other values) are defined in a separate .ph file that is generated at install time. As mr_mischief points out it is probably preferable to have these as constants so that they aren't changed from underneath you, but using constant in a separate file is going to add another layer of complexity, when all it does really is create a subroutine just like the above - the extra stuff is just to put the subroutines in the right package and make sure you don't overwrite some important symbols.

/J\