I finally caved in and downloaded Alien Bob's version of libreoffice-6.4.6-i586. It would have been nice to compile my own, but this must be the most difficult program to compile I have ever come across. Something positive to say about Porteus 4.0 i586: it has performed exceptionally well, very stable, throughout all this (50+ hours of straight compilation while the system was being used for several other tasks - all this loaded in memory). Not one single glitch. I am very impressed!
Anyway, I have moved the libreoffice part of this discussion here:
How to cause a program to look into a specific folder for its own libraries
so as to make it easier to find for those facing a similar problem.
Technical issues/questions of an intermediate or advanced nature.