Automate building external libraries #1735

Job	Run time
test_bmi_cpp (ubuntu-latest)	2m 41s
test_mpi_remote_nexus (ubuntu-latest)	2m 1s
test_bmi_cpp (macos-latest)	4m 59s
test_pet (ubuntu-latest)	2m 36s
test_pet (macos-latest)	4m 25s
test_bmi_c (ubuntu-latest)	3m 27s
test_bmi_fortran (ubuntu-latest)	3m 2s
test_bmi_multi (ubuntu-latest)	3m 39s
test_bmi_c (macos-latest)	5m 47s
test_bmi_fortran (macos-latest)	6m 9s
test_bmi_multi (macos-latest)	7m 24s
test_bmi_python (ubuntu-latest)	3m 33s
test_unit (ubuntu-latest)	4m 34s
test_bmi_python (macos-latest)	7m 22s
test_unit (macos-latest)	6m 57s
	1h 8m 36s

Provide feedback