Create generic conda toolchain

# Last check installed clang16/gfortran13/mpich
conda create -n esmf python=3.12
conda activate esmf
mamba install gfortran clangxx
mamba install mpich
mamba install xerces-c moab pyyaml cmake netcdf4
mamba install esmf # will take care of netcdf-fortran and parallelio

# On arm64 only:
#(cd $CONDA_PREFIX/bin;  ln -sf clang-20 arm64-apple-darwin20.0.0-clang++ )