Obviously there are more improvements that can be done here,
especially moving headers to .dev, but that's not entirely trivial and
probably not worth it since kde4 is old.
Upstream changes to the build system required adjusting many packages'
dependencies. On the Nixpkgs side, we no longer propagate the dependency
on cmake (to reduce closure size), so downstream dependencies had to be
adjusted for most packages that depend on kdelibs.
