Log Message:
this wants libsndfile bl3, so add it.

now the odd build failures are gone, though because of
pkgsrc wrappers, it was confusing.  "the version i found
in /usr/pkg/lib is too old", except it isn't, it was
missing from the buildlink.  the cmake output had zero
useful information about the problem (zero mention of
'sndfile' in anything but the stdout right before the
failure.)