This is a workaround for a possible compiler bug that causes constraint
recursion in the operator<=>(const optional<T>&, const U&) overload.
libstdc++-v3/ChangeLog:
PR libstdc++/104606
* include/std/optional (operator<=>(const optional<T>&, const U&)):
Reverse order of three_way_comparable_with template arguments.
* testsuite/20_util/optional/relops/104606.cc: New test.