It still insisted gcc wasn't working although the symbolic link as already suggested/done did get it to try gcc instead of a missing cc -- there were then more make test issues, missing directories and missing c header files perl needed e.g. sys/types.h.

Before switching to Ubuntu, so I can't reproduce it now, I concluded that gcc always needs a clean installation rather than a readymade delivery, i.e; either distros need to ship a slightly old gcc to make this upgrade possible or they need to schedule the compilation at the end of the first boot processing.