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

[glisse at gcc dot gnu.org]

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

--- Comment #30 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Francois-Xavier Coudert from comment #29)
> The result of "make -d --trace -j8 all-target-libstdc++-v3", in a build
> where x86_64-apple-darwin17.0.0/libstdc++-v3 was entirely removed, can be
> found here:
> https://gist.github.com/fxcoudert/b621465a794d968593bc7ed90c0fc1fb

make's I/O is not exactly a reliable way to debug multithreading issues, but
the output looks right to me.

If --disable-libstdcxx-pch works (does it?), and until someone can investigate
more, I'd be tempted to consider it a mac bug and recommend that option in
https://gcc.gnu.org/install/specific.html .