https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90441
--- Comment #23 from krux <hoganmeier at gmail dot com> --- But it's so fragile, touch any part of the code and the error disappears. Like change serial3_available to void and you also get an additional symbol: 0000000000004160 0000000000000003 T main main.cpp:8
