This is basically the same approach FreeBSD Ports takes, except they
use a patch instead of the configure flag. Since we were already
using the configure flag, I decided to go with that.
Usually I'd submit a patch upstream for this sort of thing, but I
didn't in this case because submitting a patch requires creating a
Google account and agreeing to a CLA, and because Google is
notoriously hostile to BSD patches.
Tested building for NetBSD. For FreeBSD it will work once another fix
I have in the works lands.
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