Use xfail in ptype_tagged_param.exp

Pedro pointed out that ptype_tagged_param.exp used a kfail, but an
xfail would be more appropriate as the problem appears to be in gcc,
not gdb.

gdb/testsuite/gdb.ada/ptype_tagged_param.exp

@@ -49,7 +49,7 @@ gdb_test_multiple "ptype s" "ptype s" {
     }
     -re -wrap $nodebug {
 	if {!$has_runtime_debug_info} {
-	    kfail "no debug info" $gdb_test_name
+	    xfail "no debug info" $gdb_test_name
 	} else {
 	    fail $gdb_test_name
 	}