The zynaddsubfx ebuilds all have a fixed dependency on
jack-audio-connection-kit, which is bogus when compiled without jack support:
$ ldd /usr/bin/zynaddsubfx
libz.so.1 => /lib/libz.so.1 (0x00002b237d451000)
libfltk.so.1.1 => /usr/lib64/fltk-1.1/libfltk.so.1.1
(0x00002b237d567000)
libXft.so.2 => /usr/lib/libXft.so.2 (0x00002b237d706000)
libpthread.so.0 => /lib/libpthread.so.0 (0x00002b237d81a000)
libm.so.6 => /lib/libm.so.6 (0x00002b237d934000)
libXext.so.6 => /usr/lib/libXext.so.6 (0x00002b237dab2000)
libX11.so.6 => /usr/lib/libX11.so.6 (0x00002b237dbc3000)
libfftw3.so.3 => /usr/lib/libfftw3.so.3 (0x00002b237ddd5000)
libasound.so.2 => /usr/lib/libasound.so.2 (0x00002b237dfd7000)
libstdc++.so.6 => /usr/lib/gcc/x86_64-pc-linux-gnu/4.2.0/libstdc++.so.6
(0x00002b237e19e000)
libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x00002b237e39a000)
libc.so.6 => /lib/libc.so.6 (0x00002b237e4a7000)
libfontconfig.so.1 => /usr/lib/libfontconfig.so.1 (0x00002b237e6e2000)
libfreetype.so.6 => /usr/lib/libfreetype.so.6 (0x00002b237e814000)
libXrender.so.1 => /usr/lib/libXrender.so.1 (0x00002b237e9ab000)
/lib64/ld-linux-x86-64.so.2 (0x00002b237d335000)
libXau.so.6 => /usr/lib/libXau.so.6 (0x00002b237eab5000)
libXdmcp.so.6 => /usr/lib/libXdmcp.so.6 (0x00002b237ebb7000)
libdl.so.2 => /lib/libdl.so.2 (0x00002b237ecbc000)
libxml2.so.2 => /usr/lib/libxml2.so.2 (0x00002b237edc1000)
As you can see, no run time dependency on jack. On the other hand there's no
build time dependency either (I've changed the ebuild and tested).
So the jack-audio-connection-kit dependency can be made conditional.
