Add target flags for GNU CI

[rem1776]

Description
adds the gnu mkmf template flags for prod and debug to the ci matrix

How Has This Been Tested?
CI, should be working properly. draft until all the tests are passing, needs one or two other fixes.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes

[thomas-robinson]

Are we using these flags with intel? PROD, REPRO, DEBUG?

[rem1776]

Are we using these flags with intel? PROD, REPRO, DEBUG?

No this is just for GNU: https://github.com/NOAA-GFDL/mkmf/blob/61495ce9d197a2a54bbcbb5d879fefabb3cf3c01/templates/ncrc5-gcc.mk#L87-L107
Figured I'd make a separate pr for intel.

[rem1776]

will combine this and #1346 with some more CI updates