https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82579
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> --- This is not a GCC bug, because it's the required behaviour for C++17. Use -fno-new-ttp-matching to disable it in C++17 (or use -fnew-ttp-matching to enable it in C++14 and make it ambiguous).
