Not everyone gets around to doing updates/upgrades immediately!
I concur by supporting this more disciplined (gradual) approach (mentionned below by Charles Campbell) of blocking out the code using #ifdef, then allowing the resultant "handicapped" code into the "wild" for at least 6 months.
After 6 months, any newer release is likely to have been installed and tested by those who have a critical vested interest in ensuring continuity of their preferred tools, especially if they know their OS (a.k.a. NextStep) is being gradually abandoned by upstream tool providers like Vim/GVim or others.
If the OS providers themselves consider the tool critical
enough to their own internal processes, or as part of the
User-expected toolset deployed with their OS, I am sure that they
will make their voices be heard and speak up!