Make CICE PIO compile optionally replaceable by NetCDF compile in RTs

[LarissaReames-NOAA]

Description

Since #2145 was merged, CICE is set to compile using PIO in CICE/CMakeLists.txt. However, based on the investigation in #2320 it's clear that future very long (>90 day) or high-frequency output regression test forecasts (>500 output files) that use CICE will not be possible until that issue is addressed. We need a temporary workaround that enables a regression test to set CICE_IO=NetCDF in these situations.

Solution

A simple solution should modify CICE/CMakeLists.txt to only set CICE_PIO='PIO' if it is not already set. This, along with a modification to compile.sh to provide a CMAKE flag "-DCICE_IO=NetCDF" if an option is passed from a regression test, should provide this compile-time functionality for regression tests.

Related to

N/A