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

[redi at gcc dot gnu.org]

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

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I don't see how this can happen, that header is present in the libstdc++ source
tree and there's nothing target-specific about it.