add debug flags to GNU CI and fix remaining failures

[rem1776]

Description
Adds the debug flags from the mkmf template to the gnu CI and puts in fixes for two tests that were failing.

The time_interp_external2 changes just remove the hi_tmp_src_data temporary array that was added during mixed mode. I added the temp arrays to handle the intent(out) arguments in horiz_interp, but I don't think that argument specifically needed it. This change fixes a segfault occuring during one of the unit tests.

Fixes #1480 (maybe.. 🤞)

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