libselinux: add selinux_unshare() #45

Job	Run time
build (gcc, 3.12, 3.3)	1m 43s
build (gcc, 3.12, 3.3, test-flags-override)	1m 48s
build (gcc, 3.12, 3.3, test-debug)	1m 26s
build (gcc, 3.12, 3.3, linker-bfd)	1m 37s
build (gcc, 3.12, 3.3, linker-gold)	1m 37s
build (gcc, 3.11, 3.3)	1m 37s
build (gcc, 3.10, 3.3)	2m 14s
build (gcc, 3.9, 3.3)	1m 56s
build (gcc, 3.8, 3.3)	1m 45s
build (gcc, 3.7, 3.3)	2m 15s
build (gcc, pypy3.7, 3.3)	1m 59s
build (gcc, 3.12, 3.2)	1m 36s
build (gcc, 3.12, 3.1)	1m 36s
build (gcc, 3.12, 3.0)	1m 55s
build (gcc, 3.12, 2.7)	2m 20s
build (gcc, 3.12, 2.6)	1m 50s
build (gcc, 3.12, 2.5)	1m 54s
build (clang, 3.12, 3.3)	2m 10s
build (clang, 3.12, 3.3, test-flags-override)	1m 34s
build (clang, 3.12, 3.3, test-debug)	2m 9s
build (clang, 3.11, 3.3)	2m 7s
build (clang, 3.10, 3.3)	1m 41s
build (clang, 3.9, 3.3)	2m 26s
build (clang, 3.8, 3.3)	2m 22s
build (clang, 3.7, 3.3)	1m 53s
build (clang, pypy3.7, 3.3)	2m 12s
build (clang, 3.12, 3.2)	1m 50s
build (clang, 3.12, 3.1)	1m 44s
build (clang, 3.12, 3.0)	1m 54s
build (clang, 3.12, 2.7)	2m 8s
build (clang, 3.12, 2.6)	1m 56s
build (clang, 3.12, 2.5)	1m 50s
build (gcc, 3.12, 3.3, sanitizers)	2m 4s
	1h 3m 8s

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