build,qt: Allow building Qt 5 bindings and Qt 6 bindings
* configure.ac: Remove "qt" from default_languages. Add "qt5 qt6" to default_languages. Remove "qt" from help for --enable-languages. Don't fail anymore if "qt5" and "qt6" are enabled. Warn that "qt" is deprecated if it was enabled. * lang/qt/src/Makefile.am (libqgpgme_la, libqgpgmeqt6_la): New. (lib_LTLIBRARIES): Set Qt 5 and/or Qt 6 variant of libqgpgme. (AM_CPPFLAGS): Replace with libqgpgme_la_CPPFLAGS for Qt 5 and libqgpgmeqt6_la_CPPFLAGS for Qt 6.
This makes it possible to build QGpgME simultaneously for Qt 5 and Qt 6.
By default, QGpgME is now built for all versions of Qt that are found.
Specifying "qt" as language is deprecated.
- GnuPG-bug-id: T7205