Add OpenBSD support #351

Job	Run time
freebsd (test:unit)	6m 31s
fedora (test:unit)	1m 19s
freebsd (test:examples)	5m 33s
test-examples (ubuntu-latest, 3.1)	2m 20s
fedora (test:examples)	3m 52s
openbsd (test:unit)	6m 34s
test-examples (windows-latest, 3.1)	6m 30s
test-examples (macos-latest, 3.1)	17s
openbsd (test:examples)	2m 52s
test-unit (ubuntu-latest, 2.3)	49s
test-unit (ubuntu-latest, 2.4)	48s
test-unit (ubuntu-latest, 2.5)	2m 12s
test-unit (ubuntu-latest, 2.6)	47s
test-unit (ubuntu-latest, 2.7)	49s
test-unit (ubuntu-latest, 3.0)	36s
test-unit (ubuntu-latest, 3.1)	39s
test-unit (ubuntu-latest, 3.2)	32s
test-unit (ubuntu-latest, head)	34s
test-unit (windows-latest, 2.3)	3m 19s
test-unit (windows-latest, 2.4)	4m 3s
test-unit (windows-latest, 2.5)	5m 32s
test-unit (windows-latest, 2.6)	4m 39s
test-unit (windows-latest, 2.7)	4m 46s
test-unit (windows-latest, 3.0)	4m 15s
test-unit (windows-latest, 3.1)	3m 46s
test-unit (windows-latest, 3.2)	4m 24s
test-unit (windows-latest, head)	3m 23s
test-unit (macos-latest, 2.3)	37s
test-unit (macos-latest, 2.4)	38s
test-unit (macos-latest, 2.5)	37s
test-unit (macos-latest, 2.6)	57s
test-unit (macos-latest, 2.7)	43s
test-unit (macos-latest, 3.0)	32s
test-unit (macos-latest, 3.1)	32s
test-unit (macos-latest, 3.2)	32s
test-unit (macos-latest, head)	37s
	1h 27m 26s

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