make docker compile on freebsd

Signed-off-by: Alexey Guskov <lexag@mail.ru>

reexec/command_freebsd.go

@@ -0,0 +1,23 @@
+// +build freebsd
+
+package reexec
+
+import (
+	"os/exec"
+)
+
+// Self returns the path to the current process's binary.
+// Uses os.Args[0].
+func Self() string {
+	return naiveSelf()
+}
+
+// Command returns *exec.Cmd which have Path as current binary.
+// For example if current binary is "docker" at "/usr/bin/", then cmd.Path will
+// be set to "/usr/bin/docker".
+func Command(args ...string) *exec.Cmd {
+	return &exec.Cmd{
+		Path: Self(),
+		Args: args,
+	}
+}