[Bug libstdc++/81797] gcc 7.1.0 fails to build on macOS 10.13 (High Sierra):

[fxcoudert at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81797

--- Comment #60 from Francois-Xavier Coudert <fxcoudert at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #59)
> Should be fixed on trunk, please test and confirm.

Confirmed fixed on trunk. Many thanks.

Could you please backport to gcc-7-branch and gcc-6-branch? Or okay the
backport, which I would be happy to apply.