Change the build system to enable building with Qt6
This was built with:
-DQT_MAJOR_VERSION=6
-DEXCLUDE_DEPRECATED_BEFORE_AND_AT=5.90.0
-DKF_DISABLE_DEPRECATED_BEFORE_AND_AT=0x055a00
solidhwtest is failing with: FAIL! : SolidHwTest::testPredicate() 'p6.matches(dev)' returned FALSE. () Loc: [/home/ahmad/dev6/solid/autotests/solidhwtest.cpp(336)]
An issue caused by upstream changes to how QVariant::operator== works in Qt6.