You can ignore the part related to 'gsl'. However, it seems that you have some C++ compiler issue. You may need to update your XQuartz.
On a related note, some of R-related programs in AFNI currently do not work well with R version 4.0.x on Mac OS. One solution is to downgrade your R to 3.6.x. Or run those R-related programs on a Linux computer.
Gang