[Groff] \V[envvar]: is/was there a "does-exist" concruent to 'getenv(VAR) != NULL'?

[Steffen Nurpmeso]

Hello,

i really wonder because all i can do is

  .if !'\V[GROFF_NO_MDOCMX]'' ...

but what i really would like to do is rather

  .if !d \V[GROFF_NO_MDOCMX]

so to be synchronous with $GROFF_NO_SGR.  Well i am, but only on
grotty(1) level, not in the macros, which is odd.
Wouldn't it be, even more, natural to be able to use "d" for that?

--steffen