MSVC 2019 support was dropped from Qt 6.8. Bail out early if someone
wants to build Qt with it.
One can opt out of the version check by setting the CMake variable
QT_NO_MSVC_MIN_VERSION_CHECK to ON.
Pick-to: 6.8
Change-Id: Ia1f5668e1cddcd0c9f0a8d50482fb50d0c5afe7e
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
