sac2c download package assumes cuda exists

Holden Hoover is trying to make sac2c work from the package download for ubuntu 18.04, and he is using 21.04. However, any compile he has tried fails with the linker complaining about cudart and cublas(?).

His machine does not have CUDA.

Perhaps the download instructions need improvement, or updating for a more recent ubuntu.

Meanwhile, I think the correct solution is to grant Holden access to the gitlab repository, as he is working on some sac2c-related work for me.