>> #define __UNCONST(a) ((void *)(unsigned long)(const void *)(a))
> Is this to work around gcc and/or lint being overly aggressive in
> enforcing "const"ness of a type?  Or bugs in those tools?

"Overly" aggressive?  I would speculate - and it is not entirely
uninformed speculation, as I have wanted something with equivalent
semantics myself often enough - that it is so that programs can get the
benefit of the strict checking of -Wcast-qual -Wwrite-strings while
still using interfaces (like writev()) that are broken with respect to
those checks.

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