https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117342
--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Combined build is when you build gcc together with binutils (and often other modules like gmp, mpfr, libmpc, etc.) by unpacking those into the same tree. The toplevel configure indeed doesn't check for .base64, it is gcc/configure which does that, so you should look for that in gcc/config.log. And gcc/auto-host.h then should or shouldn't define HAVE_GAS_BASE64 based on that.
