I don't know if such constant is already defined (seems not), but you could use
something like this:
type Backend {.pure.} = enum
C, CPP, OBJC, JS, PHP
const backend = when defined(cpp): Backend.CPP
elif defined(objc): Backend.OBJC
elif defined(php): Backend.PHP
elif defined(js): Backend.JS
else: Backend.C
It is a bit tough to manage this as a user, so I think it would make sense to add such constant to system lib.
