i've tried all combinations of -Fl, -Xr and -FD plugged into the Custom Options field in the IDE, but the result when compiling is always much the same:
Warning: Only one source file supported, changing source file to compile from "~/pascal/GFXterm 2.1c/libc.so.6" into "project1.lpr"
i've got two copies of the 'good' library file (uplifted from mint 19.3), one named libc.so.6, the other named libc-2.27.so, sitting in my project folder. i've also tried copying these into the lib/x86_64-linux directory of my project. but no luck. it seems that persuading the IDE to allow picking up a library from somewhere other than what it considers to be the correct location is not so easy!
an idea that did occur: could one be tricky and create a 'fake' dynamic library containing just the 6 offending symbols, convincing lazarus that the symbols are not part of the operating system? this library does not need to be functional, just provide the symbols and links that go either nowhere or to empty routines. the fake library would serve purely to 'guide' the compiling/linking process, and would be deleted/removed/renamed once that is finished.
btw: i am far from a linux expert, but i do usually manage to muddle my way through!
cheers,
rob :-)