https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78263
--- Comment #2 from Bill Schmidt <wschmidt at gcc dot gnu.org> --- From the GCC User's Manual (https://gcc.gnu.org/onlinedocs/gcc.pdf): By default, GCC also provides some additional extensions to the C++ language that on rare occasions conflict with the C++ standard. See Section 3.5 [C++ Dialect Options], page 40. Use of the ‘-std’ options listed above disables these extensions where they they conflict with the C++ standard version selected. You may also select an extended version of the C++ language explicitly with ‘-std=gnu++98’ (for C++98 with GNU extensions), or ‘-std=gnu++11’ (for C++11 with GNU extensions), or ‘-std=gnu++14’ (for C++14 with GNU extensions), or ‘-std=gnu++1z’ (for C++1z with GNU extensions).
