(only) include internals when phonon_add_executable macro is not present
(only) include internals when phonon_add_executable macro is not present

this increases compatibility between phonon <4.7 and >=4.7. for <4.7 the
internals will not be included (as they are already present), and for
>=4.7 they will be included.

note that this also prevents general double-inclusion, which is why it uses
the macro check over a version check. for phonon5 we should find a better
solution though.

KDE/phonon-gstreamer,KDE/phonon-gstreamer,shadeslayer/phonon-gstreamer,shadeslayer/phonon-gstreamer,shadeslayer/phonon-gstreamer