[Bug c++/63942] [5.0 Regression] constexpr conflicts with previous declaration

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63942

--- Comment #9 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to David Edelsohn from comment #8)
> I see -nostdinc++ -std=gnu++11 -g -O2

Ah, it seems to be triggered by -g.