Upgrading from libsndfile-1.0.17-r1 to 1.0.19 introduces new, mandatory, dependencies on libvorbis (and thus libogg too) and makes the once optional dep on flac a mandatory one. libsndfile's configure script has an option to turn (all of) them off: --disable-external-libs disable use of FLAC, Ogg and Vorbis the ebuild should have a USE flag to trigger that option and avoid linking and depending on those libraries.
Unless I'm looking at the wrong ebuild, 'minimal' useflag does exactly that.
