Thanks for your help.
Lazarus Trunk did not like the version of GDB it had been supplied and was correctly indicated in the options.
Every few years I try to get a functional linux installation but never managed to have some stable system. (whereas, for example, my old XP did work >10 years without need of a reinstall).
Always something missing or cryptic to install, and searching info resumes to comments that obviously linux is not designed for normal programmers (what about lambda users). Seems to be reserved to masochistic geeks.
Between my initial post half an hour ago and now, the installation partition that I had much pain in setting up has gone dead after a reboot (and had been stable for a week).
[CLOSED] For the next few years ...