nsenter,unshare: work around older header

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

util-linux/nsenter.c

@@ -60,6 +60,22 @@
 //usage:#endif
 
 #include <sched.h>
+#ifndef CLONE_NEWUTS
+# define CLONE_NEWUTS  0x04000000
+#endif
+#ifndef CLONE_NEWIPC
+# define CLONE_NEWIPC  0x08000000
+#endif
+#ifndef CLONE_NEWUSER
+# define CLONE_NEWUSER 0x10000000
+#endif
+#ifndef CLONE_NEWPID
+# define CLONE_NEWPID  0x20000000
+#endif
+#ifndef CLONE_NEWNET
+# define CLONE_NEWNET  0x40000000
+#endif
+
 #include "libbb.h"
 
 struct namespace_descr {