Automate building external libraries #1706

Job	Run time
test_bmi_c (ubuntu-latest)	3m 38s
test_bmi_cpp (ubuntu-latest)	2m 34s
test_bmi_c (macos-latest)	4m 30s
test_bmi_cpp (macos-latest)	3m 55s
test_bmi_fortran (ubuntu-latest)	3m 7s
test_bmi_multi (ubuntu-latest)	3m 31s
test_bmi_fortran (macos-latest)	6m 18s
test_bmi_python (ubuntu-latest)	3m 31s
test_bmi_multi (macos-latest)	5m 41s
test_bmi_python (macos-latest)	4m 17s
test_mpi_remote_nexus (ubuntu-latest)	1m 19s
test_pet (ubuntu-latest)	2m 29s
test_unit (ubuntu-latest)	4m 34s
test_pet (macos-latest)	3m 58s
test_unit (macos-latest)	8m 50s
	1h 2m 12s

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