Automate building external libraries #1701

Job	Run time
test_bmi_cpp (ubuntu-latest)	2m 38s
test_bmi_c (ubuntu-latest)	3m 24s
test_mpi_remote_nexus (ubuntu-latest)	1m 17s
test_bmi_cpp (macos-latest)	3m 50s
test_bmi_c (macos-latest)	6m 40s
test_pet (ubuntu-latest)	2m 35s
test_unit (ubuntu-latest)	4m 37s
test_pet (macos-latest)	4m 45s
test_bmi_fortran (ubuntu-latest)	2m 58s
test_unit (macos-latest)	5m 39s
test_bmi_fortran (macos-latest)	2m 16s
test_bmi_multi (ubuntu-latest)	4s
test_bmi_multi (macos-latest)	15s
test_bmi_python (ubuntu-latest)	3m 30s
test_bmi_python (macos-latest)	4m 46s
	49m 14s

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