Fixes #15688
Due to a bug, the version of the QT library was not checked at configure time for systems using pkg-config. Without any check at configure time, the build process stopped with unexplicative errors on systems with QT versions not supported.
This PR introduces the control of the version of the QT library, with a warning, or an error, at configure time, if the installed version is not supported.
Tested in all the following cases (all combinations):
- on Debian Jessie (QT 5.3.2) and on Debian Stretch (QT 5.7.1)
- with depends system (QT 5.9.7) enabled and disabled
- with
--with-gui
and--without-gui
on configure command line
Since the current 0.18 branch is affected, with compilation errors on some systems, like Debian Jessie (EOL on June 30, 2020), I suggest to include this low impact PR in 0.18.