On Mac, shared libraries typically need to have their install location as part of their "install_name" (or "id"). The link editor uses this information to hardcode the location where shared library dependencies are expected, and the dynamic loader will this fail if this information is not correct.

Okular recently (?) made the okularplugin library dependent on the okularpart (fortunately built as a shared library). This dependency is installed in the KDE plugin directory but the install_name is set to the default location for shared libraries ($prefix/lib/okularpart.dylib). As a result, the okularplugin fails to load.

This patch sets the required additional target property on both the okularpart and okularplugin shared libraries so they reflect the actual install location.

Without, loading libokularplugin.dylib fails:

can't open /opt/local/share/qt5/qml/org/kde/okular/libokularplugin.dylib (dlopen(/opt/local/share/qt5/qml/org/kde/okular/libokularplugin.dylib, 6): Library not loaded: /opt/local/lib/okularpart.dylib
  Referenced from: /opt/local/share/qt5/qml/org/kde/okular/libokularplugin.dylib
  Reason: image not found)
Exit 1

The patch solves this.