tools: check if tar supports J option

extras/tools/bootstrap

@@ -30,6 +30,11 @@ then
     echo "$1 not found"
     NEEDED="$NEEDED .$1"
 else
+    if [ "$1" = "xz" ] && ! tar PcJ /dev/null >/dev/null
+    then
+        echo "tar doesn't support xz (J option)"
+        NEEDED="$NEEDED .tar"
+    fi
     # found, need to check version ?
     [ -z "$2" ] && return # no
     # we only check GNU tools, their version have the form MAJOR.MINOR