Add library ABI suffixes on Android with Qt6

Qt6 does this in its own qt_add_library|executable macros now, and as we
don't use those we now miss the ABI suffixes. That as such works just fine,
 but we have the assumption that those suffixes are present in many places
(e.g. for the naming of the androiddeployqt dependency XML files), so
better add them here as well.