https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48559
--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> --- I'm inclined to close this as WONTFIX. The new C++17 algorithms use modern C++ and are standardised. Rather than maintain our non-standard extension, I'd prefer to deprecate our parallel mode and tell people to use C++17 instead.
