Missing check for Phonon in kdebase/runtime

[Parker Coates]

Today I did a full trunk rebuild from Qt up. My build config was a bit
messed up though, so neither Qt nor kdesupport built Phonon. The build
went fine, until it hit kdebase/runtime/phonon, which obviously failed
due to missing includes.

If Phonon is mandatory for kdebase/runtime, then the CMake file should
be checking for it. If it isn't mandatory, then obviously
kdebase/runtime/phonon should be skipped over if it isn't present.

Parker