Add podman static build

We’re now able to build a static podman binary based on a custom nix
derivation. This is integrated in cirrus as well, whereas a later target
would be to provide a self-contained static binary bundle which can be
installed on any Linux x64-bit system.

Fixes: https://github.com/containers/libpod/issues/1399

Signed-off-by: Sascha Grunert <sgrunert@suse.com>

libpod/linkmode/linkmode_dynamic.go

@@ -0,0 +1,8 @@
+// +build !static
+
+package linkmode
+
+// Linkmode returns the linking mode (static/dynamic) for the build.
+func Linkmode() string {
+	return "dynamic"
+}