Sorry for my English, I didn't mean in use, but (how should I say it) whether is was actually used by lazarus when compiling.
It seems somehow your changes weren't picked up by the compiler.
Would you like to try the following:
Open in lazarus the compiler options dialog (depending on which version you are using in the project or the run menu) and press the Test button.
Scan the output for a line containing:
Reading options from file ....
What file is mentioned there?
If it is /etc/fpc.cfg, check if there are line like
Handling option -Fl/opt/....
Interpreting option -Fl/opt/....
and further down
Using library path: /opt/....
TIA
Vincent.