Support new Vernier support in LFRic

In an upcoming change, there will be two preprocessor defines required in order to enable Vernier. We need to add these flags if required.

See:
https://code.metoffice.gov.uk/trac/lfric/ticket/4588

https://code.metoffice.gov.uk/trac/lfric/browser/LFRic/branches/dev/jedbaker/r53098_4588_timing_mod_core/infrastructure/source/utilities/timing_mod.F90?rev=53104

Start by reading the linked LFRic ticket 4588 and the referenced timing_mod.F90 revision to determine which two preprocessor defines Vernier requires. Then locate how this repository supplies build preprocessor flags; done means both flags are added when Vernier support is requested without affecting builds that do not use it.

Written by the indexing model from the issue text.