> So the issue is PCH generation (why's that re-generated at install time?).
As suggested by Marc in the PR, I've removed the @ from include/Makefile.in, and removed the leading - for lines with LN_S. 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 FX
