I had some strong issues, installing gcc-4.8.3 out of the dlang-overlay
parallel to gcc-4.7.x out of the gentoo main tree. (important packages won't
compile any more)

Now gcc-4.8.3 is stable in the main tree. I deactivated the dlang-overlay,
updated to gcc-4.8.3 and all packages compile. I'm not sure, where the error is
founded. Maybe, because I changed to 4.8.3 as main system compiler, but I don't
know exactly. I've got still 4.7.x installed.

To clearify this and save me possibly a lot of work:

Are there any differences between both gcc-4.8.3 packages apart from those,
needed to integrate gdc?

Many thanks,
Timewulf