feat(build): support Depends.OS.COMPILER (e.g. Depends.Darwin.gnu) in configure and Makefile

[johnpaulalex]

Description of changes

Enhances CIME's Depends file resolution to automatically detect and load OS-level Depends files (e.g., Depends.Darwin.gnu or Depends.Darwin):

1. CIME/BuildTools/configure.py: Adds os_name as a required 5th positional argument to copy_depends_files so it checks for Depends.<OS>.<COMPILER> and Depends.<OS> in machines_dir and copies them to <CASEROOT>.
2. CIME/case/case_setup.py: Passes os_ as the 5th positional argument during _create_macros_cmake.
3. CIME/Tools/Makefile: Adds $(CASEROOT)/Depends.$(OS) and $(CASEROOT)/Depends.$(OS).$(COMPILER) to the Makefile -include list.

Specific notes

Contributors other than yourself, if any:

• @billsacks
• @johnpaulalex

Linked issues addressed, if any:

• None

Description of generative AI usage:

• Google Antigravity was used to write the code and tests, followed by human-guided verification.

Answer Changes & Scientific Impact

• Bit-for-Bit (B4B) with baseline master
• Roundoff-level differences only
• Expected Answer Changes (ECA)

User Interface & Namelist Changes

• Namelist / Defaults modified? No
• XML / Build script changes? Yes (CIME/BuildTools/configure.py, CIME/case/case_setup.py, CIME/Tools/Makefile)

Testing planned or performed, if any:

• Executed python unit tests (python3 -m unittest CIME/tests/test_unit_case_setup.py).
• Executed build and verified cmake macro compilation under debug configurations on macOS.

CTSM / CESM baseline hash-tag: 8961a1142
PR branch hash-tag: a24867cb2

Requirements before merge:

• The code in this PR branch builds with no errors.
• The code in this PR branch runs with no errors.
• In-code documentation and Fortran docstrings updated.
• This PR either (a) does not create a need to update documentation or (b) includes required documentation updates. Which?: (a) Build infrastructure modification; no documentation updates required.

[billsacks]

This seems like a very useful feature - thank you @johnpaulalex

@jgfouca / @jasonb5 - is this something in a code path that E3SM also uses? If so, can one of you review it?

@fischer-ncar I am tentatively assigning you as reviewer from the CESM side.

[jgfouca]

@billsacks , we don't (and probably won't) use this feature. It should be harmless for you guys to add this though.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 37.16%. Comparing base (37d5018) to head (a24867c).
⚠️ Report is 192 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5026      +/-   ##
==========================================
+ Coverage   28.47%   37.16%   +8.69%     
==========================================
  Files         262      134     -128     
  Lines       38446    19629   -18817     
  Branches     8138     4161    -3977     
==========================================
- Hits        10948     7296    -3652     
+ Misses      26237    11503   -14734     
+ Partials     1261      830     -431     

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