Shaun Jackman noted that limits.h defines path_max and isn't included from

find_root_device.c.  (We #include it in busybox.h but not libbb.h, it seems.
Someday, someone's going to have to clarify for me the difference between
those two...)

libbb/find_root_device.c

@@ -19,6 +19,7 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  */
 
+#include <limits.h>
 #include <stdio.h>
 #include <string.h>
 #include <dirent.h>