https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100017
--- Comment #70 from Jonathan Wakely <redi at gcc dot gnu.org> --- We're using it to build libstdc++ so it needs to be very very close to gcc in terms of language support, and libstdc++ uses all kinds of flags like -fno-implicit-templates that are gcc-specific. I don't think it's really plausible to build libstdc++ with anything except a gcc that closely matches the version of libstdc++ being built.
