Investigate new build method for CoMorph unit tests

### Are there any linked Issues or Pull Requests?

#292

### Brief description

The CoMorph unit tests use build scripts introduced in PR 292. These are implemented in bash. It would be better to integrate them with the main LFRic build system.

### Further details of the issue.

It would make sense to add this to the SSD backlog list and for someone to liaise with @MichaelWhitall to come up with a suitable solution.

Mike wants to keep the ability to build the tests without adding any more dependencies, so any change to the build system would need to sit alongside the existing bash build scripts.

Start by reviewing the CoMorph unit-test build scripts introduced in PR 292 and the main LFRic build system. Investigate a way to integrate the tests without adding dependencies, while retaining the existing bash build scripts. Liaise with @MichaelWhitall on a suitable solution and record the work in the SSD backlog.

Written by the indexing model from the issue text.