On Tuesday 29 January 2008, maxim wexler wrote:
> > Read this guide carefully and follow it to the
> > letter:
> >
> > http://www.gentoo.org/doc/en/gcc-upgrading.xml
>
> deeper and deeper...
>
>
> "It is safe to remove the older GCC version at this
> time. If you feel the need, please issue the following
> command (as usual, substitute =sys-devel/gcc-3.4* with
> the version you want to uninstall):"
>
> gcc-4.1.2 was already emerged earlier but running gcc
> --version reveals 3.4.6, so I ran
>
> #emerge -aC =sys-devel/gcc-3.4.6-r2
>
> <...>
> --- !empty   dir /etc/eselect
> --- !empty   dir /etc/env.d/gcc
> --- !empty   dir /etc/env.d
> --- !empty   dir /etc
>  * Running 'fix_libtool_files.sh 3.4.6'
>  * Scanning libtool files for hardcoded gcc library
> paths...
> gcc-config error: Could not run/locate "gcc"
>
> :0: assertion failed: (gcc -dumpversion) | getline
>
> NEWVER)

Are you sure that you have emerged (successfully) the latest stable gcc?

> And now I don't seem to have any sort of gcc:
>
> localhost heathen # gcc --version
> gcc-config error: Could not run/locate "gcc"
>
> and emerge -uD world still fails at the same place.

Retrace your steps and follow the guide on this one.  I'm sure that you can 
recover if you ended up with no gcc, but don't know off hand what it takes to 
do it.  (I am sure that the forums are full of suggestions for this problem).

If you are certain that you have had the correct gcc installed and gcc-config 
shows that it has been selected, and you have finished with the steps 
suggested in the guide above, then run revdep-rebuild -X -p -v once more for 
good measure before you try to emerge anything else.

HTH.
-- 
Regards,
Mick