fix mkbootfs for systems that lack PATH_MAX

Change-Id: I1b841bde6de6c8e762c5fba35e6d6d701f18bb05
diff --git a/cpio/mkbootfs.c b/cpio/mkbootfs.c
index b7eb8c9..323a09d 100644
--- a/cpio/mkbootfs.c
+++ b/cpio/mkbootfs.c
@@ -44,7 +44,11 @@
 
 /* Each line in the canned file should be a path plus three ints (uid,
  * gid, mode). */
+#ifdef PATH_MAX
 #define CANNED_LINE_LENGTH  (PATH_MAX+100)
+#else
+#define CANNED_LINE_LENGTH  (1024)
+#endif
 
 static int verbose = 0;
 static int total_size = 0;