[Bug libstdc++/116070] [13/14/15 Regression] broken headers for compile with flags -std=gnu++14 -fconcepts

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116070

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #7)
> I suspect this one is a compiler bug too, since there are no concepts
> involved in that code.

Confirmed, I've added a minimal reproducer to PR 116071