[LyX/master] Allow compiling with Qt6

[Jean-Marc Lasgouttes]

Le 16/03/2021 à 18:39, Jürgen Spitzmüller a écrit :
> Am Dienstag, dem 16.03.2021 um 15:30 +0100 schrieb Jean-Marc
> Lasgouttes:
>> Needed, I do not know. I think it still works with Qt4.5 and we had
>> one user at some time, but nobody knows whether it still compiles. In
>> any case, it would be easy to fix if we got a report of broken LyX
>> with 4.5 IMO.
> 
> IIRC master has some functions that were introduced in 4.7.

I am OK with restricting to Qt 4.8. In this case, we could maybe get rid 
of the code that is only relevant to older versions.

JMarc