[Bug libstdc++/108836] std::mutex disappears in single-threaded libstdc++ builds

[pdimov at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108836

--- Comment #2 from Peter Dimov <pdimov at gmail dot com> ---
That's good to hear, but I don't think the issue is specific to mingw32. The
other report, https://github.com/boostorg/system/issues/92, was about "B&R
PLC", whatever this means. :-)