CMake build system requires a C++ compiler, although WRF-Hydro does not

[rcabell]

When running the initial CMake configuration step, an MPI C++ compiler is used to check for expected behavior. On systems not having a C++ compiler installed, this requires installing one to pass this step, even though C++ is not used in WRF-Hydro.

Expected Behavior

Building the WRF-Hydro model should not require the presence of a C++ compiler

Current Behavior

Attempting to do initial configuration of WRF-Hydro with CMake on a system without a C++ compiler results in this error, and building halts:

    --------------------------------------------------------------------------
    The Open MPI wrapper compiler was unable to find the specified compiler
    g++ in your PATH.
    
    Note that this compiler was either specified at configure time or in
    one of several possible environment variables.
    --------------------------------------------------------------------------

Possible Solution

Update CMakeLists.txt to only check for an MPI Fortran compiler.

Your Environment

• CMake 3.18.4
• GFortran 10.2
• OpenMPI 4.1.0