the package previously used PKG_OPTIONS for this, but PKG_OPTIONS
are harmful in the case that they effect the resulting ABI of
library packages. this way, things that actually need fftwl and fftwq
can depend on these sub-packages.
this also fixes fftwq on NetBSD by making it pull in libquadmath.
another thing about PKG_OPTIONS for library components is that
they mean certain components don't get tested...
