OpenMP fix in MOM_hor_visc, and enabled testing

[marshallward]

This patch fixes some issues with diagnostics in the horizontal
viscosity when OpenMP is enabled.

It also adds an OpenMP build to the tests, along with OpenMP runtime
comparison tests.

[codecov-io]

Codecov Report

Merging #1012 into dev/gfdl will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           dev/gfdl    #1012   +/-   ##
=========================================
  Coverage     43.16%   43.16%           
=========================================
  Files           213      213           
  Lines         62352    62352           
=========================================
  Hits          26915    26915           
  Misses        35437    35437

Impacted Files	Coverage Δ
src/parameterizations/lateral/MOM_hor_visc.F90	62.67% <ø> (ø)	⬆️
src/ALE/PCM_functions.F90	100% <0%> (ø)	⬆️
src/core/MOM_dynamics_unsplit.F90	92.01% <0%> (ø)	⬆️
src/user/circle_obcs_initialization.F90	91.17% <0%> (ø)	⬆️
...rameterizations/vertical/MOM_entrain_diffusive.F90	75.74% <0%> (ø)	⬆️
src/user/benchmark_initialization.F90	100% <0%> (ø)	⬆️
src/core/MOM_unit_tests.F90	66.66% <0%> (ø)	⬆️
src/tracer/MOM_tracer_hor_diff.F90	87.21% <0%> (ø)	⬆️
src/tracer/DOME_tracer.F90	65.78% <0%> (ø)	⬆️
src/tracer/MOM_neutral_diffusion_aux.F90	66.35% <0%> (ø)	⬆️
... and 59 more

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[marshallward]

Gaea regression tests: https://gitlab.gfdl.noaa.gov/ogrp/MOM6/pipelines/9077