D12674: Mark `Phonon4Qt5` dependency as optional in CMakeLists file

[Alexander Schlarb]

tundracomp added a comment.


  Could I get a new review on this please!?

REVISION DETAIL
  https://phabricator.kde.org/D12674

To: tundracomp
Cc: ltoscano, cgiboudeaux, #frameworks, michaelh, ngraham, bruns