I don't remember. I said "for a while", because I know it has been some time (maybe a year) since I've done any kind of lengthy configuration on my machine. I do update monthly with slackpkg.

A little unclear about using upgradepkg. Should I use the aforementioned link and download a pkg and then use it as follows:

It looks like your slackpkg mirror is set to 14.2, but your slackpkg+ mirror for multilib is set to -current.

Find the following line in your /etc/slackpkg/slackpkgplus.conf file and change "current" to "14.2" and then update the system.

I would probably recommend the following to make sure you have the right stuff installed. The first will uninstall all 32bit compatibility layer packages to make sure you don't have stragglers from -current that shouldn't be on 14.2. The second will make sure slackpkg has the latest info for the repos. The third will "upgrade" your gcc and glibc packages to the correct 14.2 versions. The fourth will install all missing multilib packages.

After this, you should be good to go.

That took a while, but it seems to work.

Many thanks for the assistance!

perhaps this helps
 

I have been configuring a virtual machine, and choose an old OS, scientific linux, but needed a more recent gcc compiler, so downloaded all the required stuff, and then started gcc, of course using the online recipe, having had some 'experience' building gcc twenty years ago. All went well, until during a check, the same error, that cc1 cannot find the libisl lib, so was stuck. It seems to be, - from scouring the net - happening quite alot, so what was wrong? It had to be something in the environment, but what? After cheking this and that, I finally defined LD_LIBRARY_PATH=/lib (where a soft link to the lib was) and Hallo! It worked. Make is happily chugging away further and so, this may help in other cases.