Update CMake code

[bast]

I noticed that the CMake code has not been touched in many years.

I could update that part (since I need it for my own work also) if there is interest in that. But I first wanted to check here before working on such a pull request.

[mikebedington]

There probably many parts that haven't been touched in years :-p But yes I think it would be good and might help to keep us up to date with newer clusters (compatibility with a less jurrasic-era petsc would be good on that front too). Only concern is merging in later changes from umassd. Which bits are you looking at?

[bast]

OK I will work on that. I am also a bit worried about diverging w.r.t. upstream. I am helping my researcher colleagues who are using the code but struggle with building.

[mikebedington]

Sounds good!

[bast]

The rewritten CMake code is currently here: https://github.com/bast/uk-fvcom/tree/akvaplan-updated-cmake.

I will at some point send a PR but my goal is to apply the patch to FVCOM branch but so far I have only tested it with the akvaplan branch.

[bast]

One problem in my example branch is that it only builds FVCOM as a library and not as an executable. I am working on that.

[bast]

Now it builds also the executable.