Fix Github Actions for macos system update

[apcraig]

PR checklist

• Short (1 sentence) summary of your PR:
  Fix latest problem with Github Actions for macos system update
• Developer(s):
  apcraig
• Suggest PR reviewers from list in the column to the right.
• Please copy the PR test results link or provide a summary of testing completed below.
  TBD
• How much do the PR code changes differ from the unmodified code?
  • bit for bit
  • different at roundoff level
  • more substantial
• Does this PR create or have dependencies on Icepack or any other models?
  • Yes
  • No
• Does this PR update the Icepack submodule? If so, the Icepack submodule must point to a hash on Icepack's main branch.
  • Yes
  • No
• Does this PR add any new test cases?
  • Yes
  • No
• Is the documentation being updated? ("Documentation" includes information on the wiki or in the .rst files from doc/source/, which are used to create the online technical docs at https://readthedocs.org/projects/cice-consortium-cice/. A test build of the technical docs will be performed as part of the PR testing.)
  • Yes
  • No, does the documentation need to be updated at a later time?
    • Yes
    • No
• Please document the changes in detail, including why the changes are made. This will become part of the PR commit log.

Github Actions broke again after default macos system update.

Clang was not picking up the C system files. Had to change the implementation and add -isysroot to the CFLAGS option. At the same time, removed prior implementation where the system files were linked into /usr/local/include, this was no longer working.

[eclare108213]

Really, it's a zero-character modification? Thanks for dealing with this (over and over).

[apcraig]

It's not fixed yet, need to trigger github actions to debug. First mod was adding a trivial change to create the PR, still trying to figure out what's happening. Unfortunately, I need to debug in the PR.

[eclare108213]

I see. Would it not work to PR into another branch of your own?

[apcraig]

True, I could test it in my fork first. That would require I explicitly turn on the github actions on that branch in my fork. Sort of easier just to do it in regular PR as long as others don't mind too much :)

[apcraig]

This is ready for merge.