Comment # 2 on bug 1195368 from Jiri Slaby

(In reply to Jiri Slaby from comment #1)
> qt6-core-private-devel-6.2.2-2.2

And that contains:
/usr/lib64/qt6/mkspecs/modules/qt_lib_core_private.pri
with:
QMAKE_LIBS_LIBATOMIC=

So if I do:
> %qmake6 PREFIX=%{_prefix} DISABLE_VERSION_CHECK_BY_DEFAULT=1 QMAKE_LIBS_LIBATOMIC=

The whole thing builds fine too. But that's only a workaround -- it should be
fixed somewhere in the included pri's, without the need of
qt6-core-private-devel or this workaround.