[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 #66 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes, I was afraid the RTEMS failures might be a different problem.

Are the symptoms the same? i.e. missing C++ standard library headers?

Comment 17 suggests you're seeing missing libgcc headers, which is created by a
different makefile. Maybe a similar kluge is needed in libgcc/Makefile for
build=*darwin*

What are your build, host and target triplets?