Handle Qt version > 5 in Qt AutoGen.
This patch does *NOT* include tests and documentation: There is no
Qt 6 yet. I still need this patch to work on a cmake based build
system for Qt 6.
This teaches CMake the variables
- CMAKE_GLOBAL_AUTOGEN_TARGET
- CMAKE_GLOBAL_AUTOGEN_TARGET_NAME
- CMAKE_GLOBAL_AUTORCC_TARGET
- CMAKE_GLOBAL_AUTORCC_TARGET_NAME
which control the generation of global
``autogen`` and ``autorcc`` targets.
Closes#17721