Just in case someone runs over this post, this is what you do if crossdev's stage-1 GCC compile explodes part-way through, complaining about conflicting USE options. (USE="cxx nocxx" in particular)
Change
GUSE_DISABLE_STAGE_1="${GUSE_DISABLE} -fortran nocxx -openmp"
to
GUSE_DISABLE_STAGE_1="${GUSE_DISABLE} -fortran nocxx -openmp -cxx"
That will let your stage-1 compile, and all will be well from there on.