Add support for mpifort

See https://github.com/MetOffice/lfric_core/pull/251:

> Creating a duplicate of mpif90.mk for the more modern mpifort.mk, this is only a short term solution to allow JEDI to use the more modern mpifort, this should also be considered when creating the fab build system.

Support `mpifort` (in addition to `mpif90`). It sounds like a simple copy of the mpif90 compiler wrapper is all that is required.

Start by locating the existing mpif90.mk compiler wrapper and compare it with the requested mpifort.mk support. Add the corresponding mpifort wrapper configuration, then verify that the build system recognizes mpifort in the same way as mpif90.

Written by the indexing model from the issue text.