It looks like I was missing a step out (I'd never needed it before but it seems good practice from what I've found on the net).
Prior to doing my "make xconfig" I needed to do a "make mrproper", after this everything compiled fine.
For reference it was a vanilla install of RedHat 7.1 using the version of gcc that ships with that distro and compiling 2.4.2
Thanks to all those who offered advice on this,
Joe