For what it’s worth, I figured out a solution that works:
./configure --prefix={BLD_DIR}/netcdf-c-4.6.1 FFLAGS=“-fallow-argument-mismatch” FCFLAGS=“-fallow-argument-mismatch”
I had to do this again to install MPICH and MPI, so I guess using a GFortran compiler version 10 or newer will trigger the same errors. Caveat emptor.