After some discussion with the folks at ISC, it turns out that the _ai_pad
    part of the structure was a hack to maintain binary compatibility with
    Sun binaries, and my understanding is that it's not needed generally
    on sparc systems running other operating systems. Therefore, hide this
    code behind the same set of tests as in lib/bind/include/netdb.h.
    
    This file is being imported on the vendor branch because a similar change
    (or change with similar effect) will be in the next version of BIND 9.
    
    This change will not affect other platforms in any way.