GCC 7.1 LTO linker errors

[Matt Godbolt]

Hi all,

I've been building many projects with LTO in GCC since support was
first added. I've just upgraded to GCC 7.1 (from 6.3) and all but one
of my projects build and run correctly with LTO on.

The failing project has undefined references to
std::__cxx11::basic_string<char, std::char_traits<char>,
std::allocator<char> >::~basic_string() in several files.

I'm a little perplexed at this: as best I can tell all files and
libraries are built with the same compiler, with the same flags (in
particular -std=c++1z).  I'm clearly doing something wrong though, and
I wondered if anyone had any advice on how to diagnose and debug this
issue. I've run with -v and everything looks "ok" to my untrained eye.
Sadly the codebase is huge and proprietary I'm having trouble getting
a minimal reproduction case.

Many thanks in advance,

Matt