[Bug libstdc++/66338] std::forward_as_tuple() issue with single argument

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66338

--- Comment #6 from Ville Voutilainen <ville.voutilainen at gmail dot com> ---
Should be a simple matter of doing the _NonNestedTuple checks before other
checks. Patch coming in a couple of days.