check for XOR availability

releng/releng_build_isojigdo

@@ -62,6 +62,11 @@ if [ "${XOR}" == "" -o "${DIR}" == "" -o "${IMG}" == "" ]; then
  exit 1
 fi
 
+if [ ! -x "${XOR}" ]; then
+ printf "$0: Not found or not an executable: $XOR\n"
+ exit 1
+fi
+
 # all must be set at this point
 printf "$0: Config items:"
 printf "\n\txorriso_cmd=${XOR}\n\tIN_dir=${DIR}\n\tOUT_image=${IMG}.iso"