Following the recent idea floated to consider C++20 as the default C++ language dialect by the GCC compiler rather than C++17, it was discovered that the GNU Compiler Collection itself has problems building in C++20 model.

Compared to the default C++17 (GNU++17) dialect currently used by the GCC compiler, when trying to compile GCC in C++20 mode it uncovered some issues of its own. Red Hat compiler engineer Jakub Jelinek noted on the GCC mailing list while providing patches to address C++20 build errors in GCC