Provide support for running without OpenMP

[mike-hobson]

Contact Details

@mike-hobson

Are there any linked Issues or Pull Requests?

ticket:4695

Brief description

It should be possible to build and run the LFRic codes without using OpenMP. However, at the moment, it is not.

Further details of the issue.

There are currently calls to the OpenMP library (e.g. omp_get_thread_num() and omp_get_max_threads()) inside PSyKAl-lite code that are not protected by OpenMP sentinels - so when OpenMP is turned off, it results in undefined references.

Also, it would be good to includes a test in the test suite that checks that the no OpenMP build/run still works (but I guess this would have to be in the Apps test suite - so not part of this Core ticket).

[mike-hobson]

Instances of where OpenMP (both with and without sentinels) can easily be found by running the following from the top of a working copy:

grep -ir "use omp_lib"