We implicitly checked it, because, in C++20 builds, the non-equality
relational operators are synthesized from it by the compiler, and we
test those, but we didn't check that <=> returns strong_ordering.
We now do.
Pick-to: 6.4 6.3 6.2
Task-number: QTBUG-104108
Change-Id: Ieb19a2d4cb2d600d884f4e2e89e98c6187e23872
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
1b8b802455