[Bug libstdc++/106802] New: Comparators in <functional> don't work with orderings in <compare>

[aaron at aarongraham dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106802

            Bug ID: 106802
           Summary: Comparators in <functional> don't work with orderings
                    in <compare>
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: aaron at aarongraham dot com
  Target Milestone: ---

gcc does not allow this to compile:

    std::less<>{}(std::strong_ordering::less, 0);

Even though `std::strong_ordering::less < 0` is perfectly legal and
well-formed.

It will compile this (but clang will not):

    std::less<>{}(std::strong_ordering::less, nullptr);

Godbolt link: https://gcc.godbolt.org/z/9ed16KbhP