add CAM linked lbs to exe build

[mattldawson]

Description of changes

Addition of an option to pass flags needed to link external libraries for use in CAM.

Specific notes

Contributors other than yourself, if any:

none (This is my first PR to this repo, so apologies if this is not the right way to suggest this change)

CMEPS Issues Fixed (include github issue #):

#355

Are changes expected to change answers? (specify if bfb, different at roundoff, more substantial)

No (bfb)

Any User Interface Changes (namelist or namelist defaults changes)?

No

Testing performed

Testing performed if application target is CESM:

• (recommended) CIME_DRIVER=nuopc scripts_regression_tests.py
  • machines:
  • details (e.g. failed tests):
• (recommended) CESM testlist_drv.xml
  • machines and compilers:
  • details (e.g. failed tests):
• (optional) CESM prealpha test
  • machines and compilers
  • details (e.g. failed tests):
• (other) please described in detail
  • machines and compilers
  • details (e.g. failed tests):

Testing performed if application target is UFS-coupled:

• (recommended) UFS-coupled testing
  • description:
  • details (e.g. failed tests):

Testing performed if application target is UFS-HAFS:

• (recommended) UFS-HAFS testing
  • description:
  • details (e.g. failed tests):

Hashes used for testing:

• CESM:
  • repository to check out: https://github.com/ESCOMP/CESM.git
  • branch/hash:
• UFS-coupled, then umbrella repostiory to check out and associated hash:
  • repository to check out:
  • branch/hash:
• UFS-HAFS, then umbrella repostiory to check out and associated hash:
  • repository to check out:
  • branch/hash: