[Bug c++/127627] What's the right overload resolution for ``public: X(const X&); private: explicit X(const X&) requires T::value = default;``?

[songb432 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127627

--- Comment #6 from songb432 at gmail dot com ---
(In reply to Jason Merrill from comment #5)
> Hmm, GCC assumes that non-eligible special member functions could never be
> chosen by overload resolution, but that is not the case here due to
> difference in "explicit".  And [over] doesn't consider "eligible", so it
> looks like GCC is wrong.
> 
> P0848 doesn't seem to consider differences in explicit, perhaps it should be
> included in [class.special] "kind" so that GCC's assumption is valid.

Should this be submitted to CWG?

I prefer that GCC is correct. My sentiment is that, 
if you add `static_assert(__is_trivially_copyable(X<S>));`, then you'll see
both Clang and GCC pass the assertion. But Clang just let the overload
resolution choose the non-trivial overload, that's too aggressive.
And if you change `X<S> x2 = x` to `X<S> x2(x)`, then Clang doesn't compile:
calling a private constructor.