NEW: meta/qt6

I would like to add a qt6 meta package. Nothing special here. It based
on meta/qt5. I like to have something like this to install all
dependencies in one go.


$ cat meta/qt6/pkg/DESCR
Qt is a cross-platform toolkit for developing applications, mainly GUI-based.

There's a debug version of the libraries: qt6-debug.

There are database plugins: qt6-mysql and qt6-postgresql.

People who want to use Qt6 to compile applications outside the ports tree
should note that Qt6's installation conforms to OpenBSD habits, not upstream
recommendations. Accordingly:

- libs are separated from includes.
- moc is installed as ${PREFIX}/bin/moc-qt6, in order not to conflict
with other Qt versions.
- uic is installed as ${PREFIX}/bin/uic-qt6

Generally, it's just a question of invoking:

env MOC=moc-qt6 UIC=uic-qt6 configure \
--with-qt-includes=${PREFIX}/include/X11/qt6 \
--with-qt-libraries=${PREFIX}/lib/qt6

... or, to force MOC/UIC in your make invocation:

make MOC=moc-qt6 UIC=uic-qt6

will override the Makefile contents.