Add aarch64 config defaults

[veech]

Add Linux aarch64 GNU compiler architecture to WPS

This PR adds support for Linux aarch64 systems using GNU compilers (gfortran/gcc) to the WPS configure.defaults file. The new architecture definition enables building WPS on ARM64-based Linux systems, supporting both serial and distributed memory parallel (dmpar) configurations, with and without GRIB2 support.

Key features:

• Uses gfortran and gcc compilers
• Configures appropriate flags for big-endian conversion and record markers
• Supports both serial and parallel builds
• Compatible with existing WPS configuration process

[mgduda]

@veech I may be missing something, but I think the existing Linux x86_64, gfortran stanza in configure.defaults should work equally for x86_64 and aarch64. I'd suggest creating a branch from master or the v4.6.0 tag and simply generalizing the name of the Linux x86_64, gfortran stanza to something like Linux, GNU compilers. But in any case, creating a PR from a branch and not from the head of your master branch would be good.

[veech]

For a little more context, I'm running the build within a Docker container on my Apple Silicon Mac. When running configure without the lines I added, I get this:

Will use NETCDF in dir: /wrf/LIBRARIES/netcdf
Found what looks like a valid WRF I/O library in ../WRF
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
        LANGUAGE = (unset),
        LC_ALL = (unset),
        LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
Found Jasper environment variables for GRIB2 support...
  $JASPERLIB = /wrf/LIBRARIES/grib2/lib
  $JASPERINC = /wrf/LIBRARIES/grib2/include
------------------------------------------------------------------------
Please select from among the following supported platforms.

Enter selection [1-0] : 

When changing the line in configure.defaults to:

#ARCH    Linux, GNU compilers    # serial serial_NO_GRIB2 dmpar dmpar_NO_GRIB2

I get the same as above.

Sorry about the PR from master, what's the best way to fix this? Should I create a new PR from a branch?