NetBSD fts wasn't really designed to be used in this way, and it can
produce some strange errors — e.g. I sometimes see duplicate symbols
when musl and libnbcompat define the same symbol.
More packages used musl-fts directly than the fts package anyway,
which can now be changed to use the generic fts.
Unlike netbsd.fts, musl-fts doesn't have a setup hook, so we have to
tell packages that don't know about it to link against libfts. We
could decide to copy netbsd.fts's setup hook later if we want to.
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