Add some NetBSD support

[coypoop]

I've been using podman on NetBSD, which uses some buildah code as a dependency.
I will note that buildah itself is not working (aside from building with the buildah target after these changes), but it would be nice not to have to patch the vendored buildah code in podman.

/kind other

[rhatdan]

LGTM

[rhatdan]

You should modify the Makefile to build netbsd to make sure no regressions get added to Buildah.

 grep -i freebsd Makefile 
ifeq ($(shell uname -s),FreeBSD)
# FreeBSD needs CNI until netavark is supported
FREEBSD_CROSS_TARGETS := $(filter bin/buildah.freebsd.%,$(ALL_CROSS_TARGETS))
cross: $(LINUX_CROSS_TARGETS) $(DARWIN_CROSS_TARGETS) $(WINDOWS_CROSS_TARGETS) $(FREEBSD_CROSS_TARGETS)

[rhatdan]

@dfr PTAL

[rhatdan]

@nalind @flouthoc @giuseppe @ashley-cui @l0rd @mheon PTAL

[dfr]

LGTM

[rhatdan]

/approve
/lgtm

[openshift-ci]

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