classic-only build not working well with quantization and zstd

[edwardhartnett]

When I do a classic-only build, I get:

# General
-------
Library Version:        4.6.2-development
Configured On:              Thu Sep 12 06:54:16 MDT 2024
Host System:                x86_64-pc-linux-gnu
Build Directory:            /home/ed/netcdf-fortran
Install Prefix:                 /usr/local

# Compiling Options
-----------------
Fortran Compiler:               /usr/bin/gfortran
FFLAGS:                         -g -O2 -fallow-argument-mismatch
LDFLAGS:                -L/usr/local/netcdf-c-classic/lib
C Compiler:                     gcc
CPPFLAGS:                       -I/usr/local/netcdf-c-classic/include
CFLAGS:                         -g -O2 -DLONGLONG_IS_LONG
Shared Library:             yes
Static Library:             yes
Extra libraries:            -lnetcdf -lm 

# Features
--------
F03:                            yes
Dap Support:                    no
Logging Support:                no
NetCDF-2 API:                   yes
NetCDF-4 API:                   no
CDF5 Support:                   yes
Parallel IO:                    no
NetCDF4 Parallel IO:            no
PnetCDF Parallel IO:            no
SZIP Write Support:             no
Zstandard Support:              no 
Quantize:           yes

configure: WARNING:  
configure: WARNING: ------------------------------------------
configure: WARNING: libnetcdf was built with zstd support, but HDF5_PLUGIN_PATH is not set, so zstd support is not enabled in libnetcdff. Set HDF5_PLUGIN_PATH and re-run configure if you want to enable zstd support.

configure: WARNING: You can use `nc-config --plugindir` to determine the appropriate value for HDF5_PLUGIN_PATH
configure: WARNING: ------------------------------------------
configure: WARNING:  
ed@mikado:~/netcdf-fortran$ 

Note that quantize is not available in netcdf classic formats, so should be off.