ofstub.cc: fix environ for Apple

[barracuda156]

Use the correct declaration on macOS.

[michaelonken]

Thanks Sergey,

did you try this out? I could find old references that it is required to explicitly define environ this way so I wonder whether this is still required and works on "all" Apple systems.

Thanks!

[barracuda156]

@michaelonken Yes, this way works across the board, which can be seen from a number of ports on buildbots; and CI pass for the latest macOS versions specifically for this one with the fix applied: macports/macports-ports#27063

I am not sure of the exact threshold when macOS started handling a Linux declaration for environ, but it does fail at least on some.

[michaelonken]

Merged into upstream with f4d877 (visible on public muster branch within the next days).

[barracuda156]

Thank you!