Qt5::* notation is the usual way to refer to the imported cmake targets
representing the Qt5 modules/libs. The ${Qt5*_LIBRARIES} might be from
the transitional mode, right?
PUBLIC & PRIVATE link interfaces help to speed up compilation & linking,
because libs listed in PRIVATE will stay implementation detail of the lib
and not result in consumers of the lib also having those libs in the link
list. And it also reduces the amount of includes used, so less dirs to
search headers in.
Separate commit also removes the few explicit Qt5 include dirs, which are not needed:
The include dirs are automatically added, derived from the
imported targets for the Qt5 libs that are listed in
the TARGET_LINK_LIBRARIES command.
Another separate commit makes libastro completely Qt-independent:
so far the export header was relying on QtGlobal to reuse the Q_DECL_EXPORT/Q_DECL_IMPORT defines
cmake has a macro generate_export_header which can be used instead.
(triggered by removal of broad global include statements for Qt headers in toplevel CMakeLists.txt)